Patent Description:
Knowledge of the distance and/or position of a wireless communication device can be advantageously used, for instance, for improving the communication with the wireless communication device, such as in Multiple-Input Multiple-Output (MIMO) communication scenarios. Moreover, accurate ranging of a device is important for applications in a lot of different systems, such as proximity sensors, docking control, and robot collaborations. Relative ranging is usually based on the approach of obtaining the time difference of arrival, between two communication paths, e.g. between a direct communication path and an indirect communication path involving one or more reflections. Theoretical results show that the absolute or relative ranging accuracy is proportional to the system bandwidth. However, a communication system with a large bandwidth is usually very costly with respect to the computational and power resources, for instance, because of the wideband RF costs and wideband (high sampling rate) ADC/DAC costs.

<FIG> illustrates a known approach for using a limited bandwidth for estimating a channel state by performing narrow band channel measurement over multiple frequency bands, and then splicing, i.e. combining the results. For the example of two frequency bands shown in <FIG>, an effective channel can be estimated in the following way. In a first stage, the frequency responses of the channel over the first band (referred to as "band <NUM>" in <FIG>) and over the second band (referred to as "band <NUM>" in <FIG>) are measured. In a further stage, these measurements are combined, i.e. spliced, and the channel state is estimated. More specifically, assuming that the channel response is smooth in the frequency domain, the same channel responses are expected to be identical for the two measurements within the overlapped portion of the two frequency bands, the two measurements can be combined, i.e. spliced. In doing so, a channel response over the full frequency band, i.e. covering both bands, may be obtained.

<CIT> discloses systems and techniques to reduce pilot overhead by providing common reference signals coded with cover codes that are orthogonal in time and frequency domains. Common reference signals that are coded by cover codes orthogonal in both domains can be de-spread in both the time and frequency domains for improved resolution and larger pull-in windows. Semi-uniform pilot spacing in both the frequency and time domains can be utilized. In time domain, a first pilot symbol pair is spaced by a first time interval and a second pilot symbol pair is spaced by a second time interval from the first pair, the second interval being greater than the first. In frequency domain, a first set of pilot symbols is densely placed in a selected frequency band and a second set of pilot symbols is sparsely placed surrounding and including the selected frequency band.

It is an object of the present invention to provide improved communication devices and methods for flexible channel state measurement using splicing. In particular, there is a need for such a channel state measurement scheme, because the size of the resulting effective frequency band affects, for instance, a ranging resolution (i.e. the larger the frequency band the better the ranging resolution). This object is solved by the attached independent claims and further embodiments and improvements of the invention are listed in the attached dependent claims. Hereinafter, up to the "brief description of the drawings", expressions like ". aspect according to the invention", "according to the invention", or "the present invention", relate to technical teaching of the broadest embodiment as claimed with the independent claims. Expressions like "implementation", "design", "optionally", "preferably", "scenario", "aspect" or similar relate to further embodiments as claimed, and expressions like "example", ". aspect according to an example", "the disclosure describes", or "the disclosure" describe technical teaching which relates to the understanding of the invention or its embodiments, which, however, is not claimed as such.

The invention disclosed herein generally provides a flexible channel state measurement scheme making use of frequency band splicing, i.e. combining the channel state information obtained in different, but partially overlapping frequency bands.

According to a first aspect according to the invention, a wireless transmitter is provided according to claim <NUM>.

According to a second aspect according to the invention, a wireless transmission method is provided according to claim <NUM>.

According to a third aspect according to the invention, a wireless receiver is provided according to claim <NUM>.

According to a fourth aspect according to the invention, a wireless reception method is provided according to claim <NUM>.

According to a fifth aspect according to the invention, a computer program product is provided, according to claim <NUM>.

The different aspects of the invention can be implemented in software and/or hardware.

In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:.

In the following, identical reference signs refer to identical or at least functionally equivalent features.

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures.

For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa.

<FIG> is a schematic diagram illustrating a communication system <NUM> including a wireless transmitter <NUM> according to an embodiment configured to communicate with a wireless receiver <NUM> according to an embodiment via a wireless communication channel <NUM> (also referred to as communication link <NUM>).

As illustrated in <FIG>, the wireless transmitter <NUM> comprises a processing entity, for instance, a processor <NUM> for processing data and a communication interface <NUM> for transmitting and receiving data via the communication channel <NUM>. In an embodiment, the communication interface <NUM> may comprise one or more antennas for wireless communication. The processing entity <NUM> may be implemented in hardware and/or software. The hardware may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. The wireless transmitter <NUM> may further comprise a memory <NUM>, e.g. a Flash memory <NUM>, configured to store executable program code which, when executed by the processing entity <NUM>, causes the wireless transmitter <NUM> to perform the functions and operations described herein.

Likewise, the wireless receiver <NUM> comprises a processing entity, e.g. a processor <NUM> for processing data and a communication interface <NUM> for receiving and transmitting data via the communication channel <NUM>. In an embodiment, the communication interface <NUM> may comprise one or more antennas for wireless communication. The processing entity <NUM> may be implemented in hardware and/or software. The hardware may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. The receiver apparatus <NUM> may further comprise a memory <NUM>, e.g. a Flash memory <NUM>, configured to store executable program code which, when executed by the processing entity <NUM>, causes the wireless receiver <NUM> to perform the functions and operations described herein.

As will be described in more detail below, further referring to <FIG> and <FIG>, embodiments of the wireless transmitter <NUM> and the wireless receiver <NUM> disclosed herein provide a flexible channel state measurement scheme making use of frequency band splicing, i.e. combining the channel state information obtained in different, but partially overlapping frequency bands.

More specifically, the processing entity <NUM> of the wireless transmitter <NUM> is configured to generate a first pilot signal and a second pilot signal. The communication interface <NUM> of the wireless transmitter <NUM> is configured to transmit the first pilot signal and the second pilot signal via the communication channel <NUM> to the wireless receiver <NUM>. The communication interface <NUM> of the wireless receiver <NUM> is configured to receive the first and second pilot signal transmitted via the communication channel <NUM>. As illustrated in <FIG>, the communication channel <NUM> may include a direct path and one or more reflections and the channel impulse responses measured by the wireless receiver <NUM> may exhibit one or more time delays.

<FIG> illustrates an embodiment of a flexible channel state measurement scheme implemented by the wireless transmitter <NUM> and the wireless receiver <NUM> making use of frequency band splicing, i.e. combining the channel state information obtained in different, but partially overlapping frequency bands. In the embodiment of <FIG> the wireless transmitter <NUM> is configured to transmit a first pilot or sounding signal (also referred to as ranging signal) extending in the frequency domain over a first frequency band ΨA and a second pilot or sounding signal extending over a second frequency band ΨB towards the wireless receiver <NUM>. As illustrated in <FIG>, in the frequency domain the first pilot signal and the second pilot signal overlap in a common frequency band ΨAB. Conventionally, it would only be possible to use (i.e. combine) the channel state information within the common frequency band ΨAB. However, as will be described in more detail below, embodiments disclosed herein allow to extend this band to the non-overlapping (i.e. exclusive) portions of the frequency bands ΨA and ΨB, thereby making it possible to combine the channel state information in the frequency bands ΨA and ΨB, for instance, for an improved ranging/localization operation between the wireless transmitter <NUM> and the wireless receiver <NUM>.

As illustrated in <FIG>, the first pilot signal has a first signal strength profile, i.e. spectrum over a first plurality of frequency sub-bands H1, H21, H22, H23 and the second pilot signal has a second signal strength profile over a second plurality of frequency sub-bands H21, H22, H23, H2. The first plurality of frequency sub-bands H1, H21, H22, H23 comprises a first exclusive frequency sub-band H1 exclusive to the first plurality of frequency sub-bands H1, H21, H22, H23, i.e. not overlapping with the second plurality of frequency sub-bands H21, H22, H23, H2. Likewise, the second plurality of frequency sub-bands H21, H22, H23, H2 comprises a second exclusive frequency sub-band H2 exclusive to the second plurality of frequency sub-bands H21, H22, H23, H2, i.e. not overlapping with the first plurality of frequency sub-bands H1, H21, H22, H23.

As further illustrated in <FIG>, the first plurality of frequency sub-bands H1, H21, H22, H23 and the second plurality of frequency sub-bands H21, H22, H23, H2 comprise at least three common frequency sub-bands H21, H22, H23, wherein the at least three common frequency sub-bands H21, H22, H23 comprise at least one central common frequency sub-band H22 and two boundary common frequency sub-bands H21, H23. The wireless transmitter <NUM> is configured to select the signal strength of the at least one central common frequency sub-band H22 to be smaller than a respective signal strength of the two boundary common frequency sub-bands H21, H23.

In an embodiment, the first pilot signal and the second pilot signal may be pre-specified by their code sequence and/or signal strength, in particular amplitude or power within the common frequency band ΨAB. In an embodiment, the signal strength may be an absolute power level or a relative power level between the common frequency sub-band(s) and the exclusive frequency sub-bands. Each common frequency sub-band may comprise one or more sub-carriers. The amplitude/power and/or sub-carrier pattern in each sub-band may be specified or indicated by the wireless transmitter <NUM> or the wireless receiver <NUM>.

In an embodiment, the communication interface <NUM> of the wireless transmitter <NUM> may be configured to transmit the first sounding signal and the second sounding signal (and possibly further sounding signals) sequentially or essentially parallel in time.

As already described above, in the example shown in <FIG>, the first pilot signal emitted by the wireless transmitter <NUM> may cover a first frequency band ΨA. On the basis of the first pilot signal the wireless receiver <NUM> may measure, i.e. determine first channel state information (CSI), i.e. the response of the communication channel <NUM> to the first pilot signal over the first frequency band ΨA. The second pilot signal covers the second frequency band ΨB. ΨA-B denotes the frequency band covered by the first pilot signal but not the second pilot signal. ΨB-A denotes the frequency band covered by the second pilot signal, but not the first pilot signal.

In an embodiment, the quasi-overlap frequency carrier set ΨAB can be the set of common frequency carriers in ΨA and ΨB. In a further embodiment, the quasi-overlap frequency carrier set ΨAB can be the frequency carrier in ΨA that has less than Δf seperation from at least one of frequency carriers in ΨB. The quasi-overlap frequency carrier set ΨAB can have one or more subsets. ΨAB,<NUM>, ΨAB,<NUM>, ΨAB,<NUM>.

As illustrated in <FIG>, in an embodiment, the first pilot signal transmitted over ΨAB,n in measurement A may be represented as <MAT>. The second pilot signal transmitted over ΨAB,n in measurement B may be represented as <MAT>. The power corresponding to <MAT> on subcarrier is <MAT>. At least for a subset, <MAT>, where offset<NUM> > <NUM>, offset2 > <NUM>.

For the measurement of the first pilot signal by the wireless receiver <NUM> (i.e. measurement A) due to imperfect synchronization in time tA and phase ϕA, the effective channel may be rotated by some phase shifts; <MAT> <MAT>.

The transmitted signal passes through this effective channel, so the received signal may be expressed as <MAT>.

In an embodiment, <MAT> may be predetermined by protocols. Since the wireless receiver <NUM> knows the first and second pilot signal <MAT>and <MAT>, the wireless receiver <NUM> may obtain <MAT>. By unwrapping the phases over subcarriers, and comparing them between measurement A (i.e. the first pilot signal) and B (i.e. the second pilot signal), the processing entity <NUM> of the wireless receiver <NUM> may estimate ΔtA-ΔtB (i.e. the time delay differences) and ϕA-ϕB (i.e. the phase differences). In an embodiment, the processing entity <NUM> of the wireless receiver <NUM> may be configured to generate these estimates based on a slope and an offset of the dependency of the unwrapped phases on frequency. The sub-bands or subcarriers close to ΨA-B and ΨB-A, e.g. the sub-bands H21 and H23 are very important, since they are very sensitive to ΔtA-ΔtB and ϕA-ϕB.

The sub-band(s) or subcarrier(s) in the middle of the frequency bands ΨA-B and ΨB-A, e.g. the sub-band H22, may be used for avoiding ambiguity in the unwrapping process described above. In an embodiment, the wireless receiver <NUM> may compensate the delay and phase offset difference in the measurement B (i.e. the second pilot signal), so that it can be aligned with the measurement A (i.e. the first pilot signal), as described by the following equation: <MAT>.

So, by using the channel coefficients in <MAT> the processing entity <NUM> of the wireless receiver <NUM> may obtain the channel frequency response over ΨA ∪ ΨB, which is equivalent to a wider band measurement (than both ΨA and ΨB).

The embodiments described above may be employed for ranging applications by estimating the relative or absolute delay of each channel path, sub-path or tap. For instance, Line-of-Sight (LoS) ranging may be identified and used for estimating the distance between the wireless transmitter <NUM> and the receiver <NUM>, while one or more non-LoS (NLoS) ranging estimates are used for the NLoS path recovery and virtual anchor inference. Advantageously, embodiments disclosed herein allow to provide the extended frequency bands necessary for such ranging applications.

As will be appreciated, the channel coefficients in the exclusive frequency sub-bands H1 and H2 shown in <FIG> are most sensitive to the delays and contribute most to the estimation of the LoS/NLoS delays. However, in multiple (<NUM> or more) pilot transmissions, the received signals may be corrupted by the delay misalignment. Thus, the common frequency sub-bands H21, H22, H23 allow to align two or more received pilot signals to a common time offset, based on, for instance, the relative delay ΔtA-ΔtB. The channel response over the exclusive frequency sub-bands H1 and H2 may be aligned accordingly, since the exclusive frequency and common frequency sub-bands in a pilot transmission have exact the same delay. For instance, for the measurement A, ΨA covers ΨA-B and ΨAB, so measurements on ΨA-B and ΨAB have the same delay.

As will be further appreciated, since the common frequency sub-bands H21, H22, H23 are used for the estimation of the delay (when it is a complex value, it may also take account of the phase shift), the common frequency sub-bands H21, H22, H23 are selected in an embodiment for the purpose of allowing a good estimation of the (relative) delay. As already described above, this may be achieved by allocating more power to the common frequency sub-bands H21 and H23 so that these common parts are more sensitive to this (relative) delay, and better for delay estimation. Thus, the overall signal (including both the exclusive and common frequency sub-bands) may enable improved ranging applications.

Thus, in an embodiment, the common frequency sub-bands H21, H22, H23 are used for alignment, while the exclusive frequency sub-bands H1, H2 are used for LoS/NLoS parameter (including delay) estimation. In an embodiment, these estimates can be done iteratively and their data can be combined.

In an embodiment, the first and second pilot signal, e.g. <MAT> can be predetermined by protocols implemented by the wireless transmitter <NUM> and the wireless receiver <NUM> and at least one additional variable. In an embodiment, the at least one additional variable may depend on a random seed number used by the wireless transmitter <NUM>. In an embodiment, information about this random seed number may be transmitted from the wireless transmitter <NUM> to the wireless receiver <NUM> prior, during or after the transmission of the first and/or second pilot signal. In such an embodiment, a third party receiving the first and second pilot signals is not capable of advantageously combining the information thereof as disclosed herein without knowledge of the random seed number.

In an embodiment, the power corresponding to <MAT> on subcarrier is <MAT>. Since the subcarrier in the middle of the common frequency band ΨAB may be used to avoid 2π ambiguity (as described above), a sparse sampling of subcarriers within the sub-bands may be implemented, so that adjacent sampled subcarriers (subcarrier physical power is non-zero) may have a phase shift not greater than or equal to π. In an embodiment, the effective power corresponding to <MAT> on subcarrier is <MAT> and may be determined by sampling the subcarrier spacing. For instance, in an embodiment, the first and second pilot signal <MAT> may occupy <NUM> subcarrier over K consecutive subcarriers, so that <MAT>. Since more effective power can be allocated to the subcarrier in ΨA-B, and ΨB-A, the channels, which are more relevent to delay or phase difference estimation, may lead to better localization accuracy.

In a further embodiment, the first and/or second pilot signal, i.e. <MAT>, X = A or B can be pre-coded in the frequency/spatial domain by the wireless transmitter <NUM>, so as to minimize the impact of the pilot signal on a further concurrent wireless transmission.

In an embodiment, the common frequency sub-bands may have more than one subcarriers, so that the measurement within this set has frequency diversity.

<FIG> shows a flow diagram illustrating steps of a wireless transmission method <NUM> for communication via the communication channel <NUM>. The wireless transmission method <NUM> comprises a first step <NUM> of generating the first pilot signal having a first signal strength profile over the first plurality of frequency sub-bands H1, H21, H22, H23 and the second pilot signal having a second signal strength profile over the second plurality of frequency sub-bands H21, H22, H23, H2. Moreover, the method <NUM> comprises the step <NUM> of transmitting the first pilot signal and the second pilot signal via the communication channel to the wireless receiver <NUM>. As already described above, the first plurality of frequency sub-bands H1, H21, H22, H23 comprises the first exclusive frequency sub-band H1 exclusive to the first plurality of frequency sub-bands H1, H21, H22, H23. The second plurality of frequency sub-bands H21, H22, H23, H2 comprises the second exclusive frequency sub-band H2 exclusive to the second plurality of frequency sub-bands H21, H22, H23, H2. The first plurality of frequency sub-bands H1, H21, H22, H23 and the second plurality of frequency sub-bands H21, H22, H23, H2 comprise at least three common frequency sub-bands H21, H22, H23, wherein the at least three common frequency sub-bands H21, H22, H23 comprise at least one central common frequency sub-band H22 and two boundary common frequency sub-bands H21, H23. A respective signal strength of the at least one central common frequency sub-band H22 is smaller than a respective signal strength of the two boundary common frequency sub-bands H21, H23.

<FIG> shows a flow diagram illustrating steps of a wireless reception method <NUM> for communication via the communication channel <NUM>. The wireless reception method <NUM> comprises the step <NUM> of receiving the first pilot signal and the second pilot signal via the communication channel <NUM> from the wireless transmitter <NUM>. As already described above, the first pilot signal has a first signal strength profile over the first plurality of frequency sub-bands H1, H21, H22, H23 and the second pilot signal has a second signal strength profile over the second plurality of frequency sub-bands H21, H22, H23, H2. The first plurality of frequency sub-bands H1, H21, H22, H23 comprises a first exclusive frequency sub-band H1 exclusive to the first plurality of frequency sub-bands H1, H21, H22, H23. The second plurality of frequency sub-bands H21, H22, H23, H2 comprises a second exclusive frequency sub-band H2 exclusive to the second plurality of frequency sub-bands H21, H22, H23, H2. The first plurality of frequency sub-bands H1, H21, H22, H23 and the second plurality of frequency sub-bands H21, H22, H23, H2 comprise at least three common frequency sub-bands H21, H22, H23, wherein the at least three common frequency sub-bands H21, H22, H23 comprise at least one central common frequency sub-band H22 and two boundary common frequency sub-bands H21, H23. A respective signal strength of the at least one central common frequency sub-band H22 is smaller than a respective signal strength of the two boundary common frequency sub-bands H21, H23.

The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the invention (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described apparatus embodiment is merely exemplary.

Claim 1:
A wireless transmitter (<NUM>), comprising:
a) a processing entity (<NUM>) configured to generate a first pilot signal having a first signal strength profile over a first plurality of adjacent frequency sub-bands (H1, H21, H22, H23) and a second pilot signal having a second signal strength profile over a second plurality of adjacent frequency sub-bands (H21, H22, H23, H2); and
a communication interface (<NUM>) configured to transmit the first pilot signal and the second pilot signal via a communication channel (<NUM>) to a wireless receiver (<NUM>),
wherein the first plurality of frequency sub-bands (H1, H21, H22, H23) comprises a first exclusive frequency sub-band (H1) exclusive to the first plurality of frequency sub-bands (H1, H21, H22, H23),
wherein the second plurality of frequency sub-bands (H21, H22, H23, H2) comprises a second exclusive frequency sub-band (H2) exclusive to the second plurality of frequency sub-bands (H21, H22, H23, H2),
wherein the first plurality of frequency sub-bands (H1, H21, H22, H23) and the second plurality of frequency sub-bands (H21, H22, H23, H2) comprise at least three common frequency sub-bands (H21, H22, H23),
wherein the at least three common frequency sub-bands (H21, H22, H23) comprise at least one central common frequency sub-band (H22) and two boundary common frequency sub-bands (H21, H23), wherein one of the two boundary common frequency sub-bands (H21) is placed at a lower frequency side of and adjacent to the central common frequency sub-band (H22), and the other of the two boundary common frequency sub-bands (H23) is placed at a higher frequency side of and adjacent to the central common frequency sub-band (H22), and
wherein, in each of the first and second signal strength profiles, respectively, a respective signal strength of the at least one central common frequency sub-band (H22) is smaller than a respective signal strength of the two adjacent boundary common frequency sub-bands (H21, H23).