TECHNICAL FIELD

The present disclosure relates to a receiver for wireless communication with a transmitter and a method for operating a receiver. The present disclosure further relates to a transmitter for wireless communication with a receiver and a method for operating a transmitter.

BACKGROUND

The present disclosure is in the field of high-resolution communication devices and short- distance communication devices, in particular high-resolution short-distance communication devices (e.g. ultra high-resolution short-distance communication devices) that are configured for wireless communication. A high-resolution communication device may be a portable device, such as headsets, in particular headsets for virtual reality (e.g. virtual reality gaming).

SUMMARY

In particular, embodiments of the present disclosure are based on the following considerations made by the inventors:

High-resolution communication devices and high-resolution short-distance communication devices require receivers with a high data rate and a high power consumption. The data rate may be increased by using wide-band communications (e.g. ultra-wide band communications), which require a complex receiver design with a high power consumption. For a high-resolution short-distance communication, the communication may be wire-bound, e.g. via a cable connection between a transmitter and the receiver. However, this limits the movement capability of the receiver, respectively, the portable device comprising the receiver, e.g. due to the length of the cable connection. Therefore, a wireless communication is preferred. Short- distance communication devices are often used for indoor communications. As a result, the channel for the wireless communication of a transmitter to the receiver of such a short-distance communication device becomes a fading channel because of the multi-paths caused by reflection (e.g. on objects, walls etc.) in the indoor area.

In order to achieve a receiver with a high data rate, a receiver configured for wireless communication based on millimeter electromagnetic waves (i.e. electromagnetic waves with a millimeter wavelength) may be used. That is, it is proposed to use millimeter wave bands for the wireless communication between a transmitter and the receiver, in order to increase the data rate of the wireless communication. This has the drawback that the amplitude of a wireless signal transmitted in the form of millimeter electromagnetic waves via a channel is typically attenuated very strongly by the channel. As a result, the amplitude of such a wireless signal received by the receiver (after propagating via the channel) is much smaller compared to the wireless signal at the time of transmittal from the transmitter (before propagation via the channel). In other words, the signal level of the wireless signal received by the receiver is very low. To overcome this, the transmitter may focus the wireless signal to the receiver. This reduces the attenuation effect of the channel on the wireless signal (transmitted in the form of millimeter waves) and, thus, increases the amplitude of the wireless signal received by the receiver compared to the case of no focusing. That is, the transmitter may focus the wireless signal to the receiver in order to increase the signal level of the received signal compared to the case of no focusing. This kind of focusing may be referred to as spatial wave-focusing, namely focusing the energy to the receiver.

In order to allow such a focusing, the effects of the channel (channel effects) have to be known. The channel effects comprise the attenuation of the amplitude of the wireless signal when propagating via the channel and a phase change between the phase of the wireless signal transmitted by the transmitter (i.e. the phase of the wireless signal before propagation via the channel) and the phase of the wireless signal received by the receiver from the transmitter via the channel (i.e. the phase of the wireless signal after propagation via the channel). Thus, to overcome the channel effects, a good estimation of the channel needs to be done at the receiver side. This requires estimating the attenuation of the amplitude of the received wireless signal and the phase change between the phase of the transmitted wireless signal and the phase of the received wireless signal at the receiver side. Such an estimation may be complex and power consuming. Therefore, the receiver may comprise a size and weight unsuitable for a portable device due to the electronic circuit for such estimation. In addition, the receiver needs to be provided with sufficient electrical energy. This may be a problem when the receiver is part of a portable device which use a battery as an electrical energy source. Therefore, either the time during which the batter sufficiently provides electrical energy is reduced or the portable device becomes bulky and heavy, when using a battery with a higher capacity. In view of the above-mentioned problems and disadvantages, embodiments of the present disclosure aim to improve a receiver for use in a wireless communication. In particular, an objective is to provide an improved receiver that may be configured for a wireless indoor communication based on millimeters waves to achieve a high data rate and that is improved with respect to the above drawbacks and disadvantages, in particular high complexity and high power consumption. A further objective may be to provide a receiver configured for a wireless communication based on millimeter waves and suitable for a portable device, such as headsets, in particular headsets for virtual reality (e.g. virtual reality gaming).

These and other objectives are achieved by the embodiments of the disclosure as described in the enclosed independent claims. Advantageous implementations of the embodiments of the disclosure are further defined in the dependent claims.

A first aspect of the present disclosure provides a receiver for wireless communication with a transmitter. The receiver is configured to receive a wireless signal from the transmitter via a first channel and determine channel estimation information by estimating an attenuation of an amplitude of the received wireless signal. The receiver is further configured to transmit the channel estimation information to the transmitter via a second channel, wherein the channel estimation information comprises the estimated attenuation of the amplitude of the received wireless signal without information on a phase change between a phase of the received wireless signal and a phase of the wireless signal transmitted by the transmitter.

In other words, the present disclosure proposes to omit, at the receiver side, the estimation of the phase change between the phase of the received wireless signal and the phase of the wireless signal transmitted by the transmitter. As a result, the complexity and power consumption of the receiver is reduced, because the receiver does not need to comprise the circuitry for the phase change estimation. Nevertheless, the receiver still allows the transmitter to focus the wireless signal to the receiver, because the receiver is configured to estimate the attenuation of the amplitude of the wireless signal and transmit the estimated attenuation in form of the channel estimation information to the transmitter. Thus, the transmitter receives a feedback about the first channel from the receiver and may estimate on the basis of this feedback the phase change caused by the first channel in order to be able to perform the focusing. As a result, the receiver is suited for a wireless communication based on millimeters electromagnetic waves without the drawback of a strong attenuation of the wireless signal by the first channel. Namely, this drawback may be reduced, in particular overcome, by focusing, which may be performed by the transmitter due to the feedback on the first channel in the form of the estimated attenuation. In particular, the receiver allows, by transmitting the estimated attenuation to the transmitter via the second channel, the transmitter to perform a precoding, in particular a time reversal precoding, of data before transmitting the data in the form of the wireless signal achieving the focusing, in particular the spatial wave-focusing. In addition, due to the precoding, in particular time reversal precoding, a temporal wave focusing may be achieved, which reduces the effect of multi-paths in the case of a wireless indoor communication. In the light of the above, the receiver of the first aspect solves the objectives of the present disclosure. The terms “precoding” and “prefiltering” may be used as synonyms.

In particular, the receiver is configured to transmit the channel estimation information via the second channel to the transmitter for estimating, at the transmitter side based on the estimated attenuation, the phase change between the phase of the wireless signal received by the receiver and the phase of the wireless signal transmitted by the transmitter.

The attenuation of the amplitude of the received wireless signals is caused by the first channel. Due to this attenuation, the amplitude of a wireless signal transmitted via the first channel is greater at the transmitter than at the receiver. That is, the amplitude of a wireless signal after propagation via the first channel (amplitude of wireless signal received by receiver) is smaller/lower than the amplitude of the wireless signal before propagation via the first channel (amplitude of wireless signal transmitted/output by the transmitter). The attenuation caused by the first channel of the amplitude of the wireless signal may be referred to as “amplitude of the channel”. That is, the effect of the first channel on the amplitude of a wireless signal propagating via the first channel may be referred to as the “amplitude of the first channel”.

The receiver may be a non-coherent receiver. In particular, the receiver does not comprise a local oscillator and/or IQ modulator for channel estimation of the first channel, in particular estimation of a phase change between the phase of the wireless signal received by the receiver and the phase of the wireless signal transmitted by the transmitter. That is, the receiver is a receiver without a local oscillator and/or IQ modulator for channel estimation of the first channel, in particular estimation of the phase change. The first channel may be referred to as “main channel”. The second channel may be referred to as “feedback channel”.

In an implementation form of the first aspect, the receiver is configured to estimate the attenuation of the amplitude of the received wireless signal by estimating, for two or more sub bands of the first channel, the attenuation of the amplitude of the received wireless signal.

Thus, estimating an attenuation of the amplitude of the received wireless signal may correspond to estimating, for two or more sub-bands, in particular for all sub-bands, of the first channel, an attenuation of the amplitude of the received wireless signal. In other words, estimating an attenuation of the amplitude of the received wireless signal may correspond to estimating an attenuation of the amplitude of the received wireless signal over two or more sub-bands, in particular all sub-bands, of the first channel.

The receiver may be configured to estimate a vector of attenuations, wherein each element/entry of the vector corresponds to a sub-band of the two or more sub-bands of the first channel. Therefore, the elements of the vector and, thus, the estimated attenuations for the two or more sub-bands of the first channel may form the estimated attenuation of the amplitude of the received wireless signal. The estimation may be performed for all sub-bands (respectively each sub-band) of the first channel. The two or more sub-bands may be defined by a protocol used by the receiver for communicating via the first channel.

The vector of attenuations may not be absolute. That is, the elements of the vector may be relative to a certain level, which may be the noise level. Therefore, estimating an attenuation of the amplitude of the received wireless signal may correspond to estimating the relative attenuation of the amplitude of the received wireless signal over the two or more sub-bands of the first channel.

The transmitter may be configured to transmit the wireless signal using millimeter electromagnetic waves. The transmitter may be configured to transmit the wireless signal with a frequency above 20 GHz. The receiver may be configured to transmit the channel estimation information, in particular the estimated attenuation of the amplitude of the received wireless signal, via the second channel to the transmitter with a frequency below 6 GHz. In particular, the receiver is configured to transmit the channel estimation information in the form of a wireless signal (may be referred to as “wireless feedback signal”) to the transmitter.

In particular, the first channel is a wideband, more particular ultra-wideband, channel. The first channel may be an above-20 GHz channel respectively a channel with a (center) frequency above 20 GHz. The first channel defines the characteristics of a first link between the transmitter and the receiver for transmitting a wireless signal from the transmitter to the receiver. Thus, the first link may be a wideband link, in particular an ultra-wideband link. The first link may be a multi-paths link, in particular in case of an indoor wireless communication. In particular, the first channel may be a fading channel. The first link may be referred to as “main link”.

The second channel may be a narrow/low bandwidth channel. The second channel may be a sub-6 GHz channel respectively a channel with a (center) frequency below 6 GHz. In particular, the bandwidth of the second channel may be smaller than the bandwidth of the first channel. The second channel may use the same frequency of the first channel but with a more robust transmission scheme and lower rate. The second channel defines the characteristics of a second link between the transmitter and the receiver for wireless transmission of the channel estimation information from the receiver to the transmitter. Thus, the second link may be a narrow/low bandwidth link The second link may be a low multi-paths link. In particular, the second channel may be a clear channel. The second link may be defined as “feedback link”.

In an implementation form of the first aspect, the receiver is configured to estimate the attenuation of the amplitude of the received wireless signal by detecting the amplitude of the received wireless signal.

In particular, the receiver comprises an amplitude detector for detecting the amplitude of the received wireless signal. The amplitude detector may be an envelope detector.

This reduces the complexity and power consumption of the receiver, because a detector for detecting the amplitude of the received wireless signal, such as an envelope detector, does not comprise or correspond to a complex and a high-power consuming circuitry. As a result, the receiver may be smaller in size and reduced in weight, which is advantageous when using the receiver in a portable device. In particular, detecting the amplitude of the received wireless signal corresponds to detecting the amplitude of the received wireless signal for each sub-band of the set of sub-bands of interest.

In an implementation form of the first aspect, the receiver is further configured to receive a wireless training signal from the transmitter via the first channel, the wireless training signal having an initial amplitude known by the receiver, wherein the receiver is configured to estimate the attenuation of the amplitude of the received wireless signal by estimating an attenuation of an amplitude of the received wireless training signal.

The wireless training signal may be referred to as “sounding signal”.

In an implementation form of the first aspect, the receiver is configured to detect the amplitude of the received wireless training signal; and compute a difference between the amplitude of the received wireless training signal and the initial amplitude of the wireless training signal to estimate the attenuation of the amplitude of the received wireless training signal

In an implementation form of the first aspect, the receiver is configured to compute, in the frequency domain, the difference between the amplitude of the received wireless training signal and the initial amplitude of the wireless training signal to generate an absolute value of a frequency response of the first channel, wherein the channel estimation information comprises the absolute value of the frequency response of the first channel as an indicator of the estimated attenuation of the amplitude of the received wireless signal.

In particular, computing, in the frequency domain, the difference between the amplitude of the received wireless training signal and the initial amplitude of the wireless training signal may comprise or correspond to computing a ratio between a Fourier Transform (FT) of the received wireless training signal and a Fourier Transform of the wireless training signal having the initial amplitude. In particular, the absolute value of the frequency response of the first channel may equal to the absolute value of the ratio between the Fourier Transform (FT) of the received wireless training signal and the Fourier Transform of the wireless training signal having the initial amplitude. The ratio may correspond to the division of the Fourier Transform of the received wireless training signal divided by the Fourier Transform of the wireless training signal having the initial amplitude. According to an embodiment, the Fourier Transform may be a Discrete Fourier Transform (DFT), e.g. a Fast Fourier Transform (FFT). That is, the absolute value of the frequency response of the first channel may equal to the absolute value of a ratio between a Fast Fourier Transform of the received wireless training signal and a Fast Fourier Transform of the wireless training signal having the initial amplitude.

In order to achieve the receiver according to the first aspect of the present disclosure, some or all of the implementation forms and optional features of the first aspect, as described above, may be combined with each other.

A second aspect of the present disclosure provides a method for operating a receiver. The method comprises: receiving a wireless signal from a transmitter via a first channel; determining channel estimation information by estimating an attenuation of an amplitude of the received wireless signal; and transmitting the channel estimation information to the transmitter via a second channel. The channel estimation information comprises the estimated attenuation of the amplitude of the received wireless signal without information on a phase change between a phase of the received wireless signal and a phase of the wireless signal transmitted by the transmitter.

The receiver may be the receiver according to the first aspect or any of its implementation forms.

The implementation forms and optional features of the receiver according to the first aspect are correspondingly valid for the method according to the second aspect.

In an implementation form of the second aspect, the method comprises: estimating the attenuation of the amplitude of the received wireless signal by estimating, for two or more sub bands of the first channel, the attenuation of the amplitude of the received wireless signal.

In an implementation form of the second aspect, the method comprises: estimating the attenuation of the amplitude of the received wireless signal by detecting the amplitude of the received wireless signal.

In an implementation form of the second aspect, the method comprises: receiving a wireless training signal from the transmitter via the first channel, the wireless training signal having an initial amplitude known by the receiver, and estimating the attenuation of the amplitude of the received wireless signal by estimating an attenuation of an amplitude of the received wireless training signal.

In an implementation form of the second aspect, the method comprises: detecting the amplitude of the received wireless training signal; and computing a difference between the amplitude of the received wireless training signal and the initial amplitude of the wireless training signal to estimate the attenuation of the amplitude of the received wireless training signal.

In an implementation form of the second aspect, the method comprises: computing, in the frequency domain, the difference between the amplitude of the received wireless training signal and the initial amplitude of the wireless training signal to generate an absolute value of a frequency response of the first channel, wherein the channel estimation information comprises the absolute value of the frequency response of the first channel as an indicator of the estimated attenuation of the amplitude of the received wireless signal.

The method of the second aspect and its implementation forms and optional features achieve the same advantages as the receiver of the first aspect and its respective implementation forms and respective optional features.

In order to achieve the method according to the second aspect of the present disclosure, some or all of the implementation forms and optional features of the second aspect, as described above, may be combined with each other.

A third aspect of the present disclosure provides a transmitter for wireless communication with a receiver. The transmitter is configured to transmit a wireless signal to the receiver via a first channel and receive channel estimation information from the receiver via a second channel. The channel estimation information comprises an estimated attenuation of an amplitude of the wireless signal. The transmitter is further configured to estimate a phase change between a phase of the wireless signal received by the receiver and a phase of the wireless signal transmitted by the transmitter, based on the estimated attenuation of the amplitude of the wireless signal. The transmitter of the second aspect allows omitting, at the receiver side, the estimation of the phase change between the phase of the wireless signal received by the receiver and the phase of the wireless signal transmitted by the transmitter. As a result, the complexity and power consumption of the receiver is reduced, because the receiver does not need to comprise the circuitry for the phase change estimation. Nevertheless, the transmitter is able to focus the wireless signal to the receiver, because the transmitter is configured to receive the estimated attenuation in form of the channel estimation information from the receiver. Thus, the transmitter may estimate on the basis of this feedback the phase change caused by the first channel in order to be able to perform the focusing. As a result, the receiver is suited for a wireless communication based on millimeters electromagnetic waves without the drawback of a strong attenuation of the wireless signal by the first channel. Namely, this drawback may be reduced, in particular overcome, by focusing, which may be performed by the transmitter.

The phase change between the phase of the wireless signal received by the receiver and the phase of the wireless signal transmitted by the transmitter is caused by the first channel. Due to this phase change, the phase of a wireless signal transmitted via the first channel is different at the transmitter and at the receiver. That is, the phase of a wireless signal after propagation via the first channel (phase of the wireless signal received by receiver) is different to the phase of the wireless signal before propagation via the first channel (phase of the wireless signal transmitted/output by the transmitter). The phase change caused by the first channel of the phase of the wireless signal may be referred to as “phase of the channel”. That is, the effect of the first channel on the phase of a wireless signal propagating via the first channel may be referred to as the “phase of the first channel”.

The transmitter may be configured to perform amplitude modulation for generating the wireless signal. Thus, the data comprised by the wireless signal may be modulated on the amplitude of the wireless signal.

In an implementation form of the third aspect, the transmitter is configured to estimate the phase change based on the estimated attenuation by estimating, for two or more sub-bands of the first channel, a phase change based on the estimated attenuation of the respective sub-band.

Therefore, estimating a phase change based on the estimated attenuation may correspond to estimating, for two or more sub-bands, in particular for all sub-bands, of the first channel, a phase change based on the estimated attenuation of the respective sub-band. In other words, estimating a phase change based on the estimated attenuation may correspond to estimating a phase change between the phase of the wireless signal received by the receiver and the phase of the wireless signal transmitted by the transmitter over two or more sub-bands, in particular all sub-bands, of the first channel.

The transmitter may be configured to estimate a vector of phase changes based on the estimated attenuation, wherein each element/entry of the vector corresponds to a sub-band of the two or more sub-bands of the first channel. Therefore, the elements of the vector and, thus, the estimated phase changes for the two or more sub-bands of the first channel may form the estimated phase change between the phase of the wireless signal received by the receiver and the phase of the wireless signal transmitted by the transmitter. The estimation may be performed for all sub-bands (respectively each sub-band) of the first channel. The two or more sub-bands may be defined by a protocol used by the transmitter for communicating via the first channel.

In an implementation form of the third aspect, the transmitter is configured to estimate the phase change by performing one or more phase reconstruction algorithms based on the estimated attenuation.

The terms “phase retrieval algorithm” and “phase reconstruction algorithm” may be used as synonyms.

In an implementation form of the third aspect, the one or more phase reconstruction algorithms comprise at least one of one or more sparse algorithms and one or more Griffin-Lim algorithms.

In an implementation form of the third aspect, the transmitter is configured to receive the channel estimation information comprising an absolute value of a frequency response of the first channel as an indicator of the estimated attenuation from the receiver via the second channel; and perform, in the frequency domain, the one or more phase reconstruction algorithms based on the absolute value of the frequency response of the first channel to estimate the phase change. In an implementation form of the third aspect, the transmitter is configured to apply, based on the estimated phase change and the received estimated attenuation, precoding to data before transmitting the data in the form of a wireless signal to the receiver via the first channel.

In particular, the precoding is time reversal precoding. That is, the transmitter may be configured to apply, based on the estimated phase change and the received estimated attenuation, time reversal precoding to data before wirelessly transmitting the data in the form of a wireless signal via the first channel to the receiver.

Therefore, the transmitter may achieve the focusing, in particular the spatial wave-focusing. In addition, due to the precoding, in particular time reversal precoding, a temporal wave focusing may be achieved, which reduces the effect of multi-paths in the case of a wireless indoor communication.

In an implementation form of the third aspect, the transmitter is configured to transmit a wireless training signal to the receiver via the first channel.

In an implementation form of the third aspect, the transmitter is configured to transmit a data frame to the receiver via the first channel by transmitting a wireless data signal comprising the data frame and a wireless training signal to the receiver via the first channel.

The transmitter of the third aspect and its implementation forms and optional features achieve the same advantages as the receiver of the first aspect and its respective implementation forms and respective optional features.

In order to achieve the transmitter according to the third aspect of the present disclosure, some or all of the implementation forms and optional features of the third aspect, as described above, may be combined with each other.

A fourth aspect of the present disclosure provides a method for operating a transmitter. The method comprises: transmitting a wireless signal to a receiver via a first channel and receiving channel estimation information from the receiver via a second channel. The channel estimation information comprises an estimated attenuation of an amplitude of the wireless signal. The method further comprises: estimating a phase change between a phase of the wireless signal received by the receiver and a phase of the wireless signal transmitted by the transmitter, based on the estimated attenuation of the amplitude of the wireless signal.

The transmitter may be the transmitter according to the third aspect or any of its implementation forms.

The implementation forms and optional features of the transmitter according to the third aspect are correspondingly valid for the method according to the fourth aspect.

In an implementation form of the fourth aspect, the method comprises: estimating the phase change based on the estimated attenuation by estimating, for two or more sub-bands of the first channel, a phase change based on the estimated attenuation of the respective sub-band.

In an implementation form of the fourth aspect, the method comprises: estimating the phase change by performing one or more phase reconstruction algorithms based on the estimated attenuation.

In an implementation form of the fourth aspect, the one or more phase reconstruction algorithms comprise at least one of one or more sparse algorithms and one or more Griffm-Lim algorithms.

In an implementation form of the fourth aspect, the method comprises: receiving the channel estimation information comprising an absolute value of a frequency response of the first channel as an indicator of the estimated attenuation from the receiver via the second channel; and performing, in the frequency domain, the one or more phase reconstruction algorithms based on the absolute value of the frequency response of the first channel to estimate the phase change.

In an implementation form of the fourth aspect, the method comprises: applying, based on the estimated phase change and the received estimated attenuation, precoding to data before transmitting the data in the form of a wireless signal to the receiver via the first channel.

In an implementation form of the fourth aspect, the method comprises: transmitting a wireless training signal to the receiver via the first channel. In an implementation form of the fourth aspect, the method comprises: transmitting a data frame to the receiver via the first channel by transmitting a wireless data signal comprising the data frame and a wireless training signal to the receiver via the first channel.

The method of the fourth aspect and its implementation forms and optional features achieve the same advantages as the transmitter of the third aspect and its respective implementation forms and respective optional features.

In order to achieve the method according to the fourth aspect of the present disclosure, some or all of the implementation forms and optional features of the fourth aspect, as described above, may be combined with each other.

A fifth aspect of the present disclosure provides a non-transitory storage medium storing executable program code which, when executed by a processor, causes the method according to the second aspect or any of its implementation forms to be performed.

A sixth aspect of the present disclosure provides a non-transitory storage medium storing executable program code which, when executed by a processor, causes the method according to the fourth aspect or any of its implementation forms to be performed.

A seventh aspect of the present disclosure provides a computer program comprising program code for performing when implemented on a processor, a method according to the second aspect or any of its implementation forms.

A eighth aspect of the present disclosure provides a computer program comprising program code for performing when implemented on a processor, a method according to the fourth aspect or any of its implementation forms.

A ninth aspect of the present disclosure provides a computer comprising a memory and a processor, which are configured to store and execute program code to perform the method according to the second aspect or any of its implementation forms. A tenth aspect of the present disclosure provides a computer comprising a memory and a processor, which are configured to store and execute program code to perform the method according to the fourth aspect or any of its implementation forms.

The non-transitory storage medium of the fifth aspect, the computer program of the seventh aspect and the computer of the ninth aspect each achieve the same advantages as the method of the second aspect and its respective implementation forms and respective optional features.

The non-transitory storage medium of the sixth aspect, the computer program of the eighth aspect and the computer of the tenth aspect each achieve the same advantages as the method of the fourth aspect and its respective implementation forms and respective optional features.

An eleventh aspect of the present disclosure provides a system. The system comprises a transmitter according the third aspect of the present disclosure or any of its implementation forms and optional features. The system further comprises a receiver according the first aspect of the present disclosure or any of its implementation forms and optional features. The transmitter is configured to transmit a wireless signal to the receiver via a first channel.

A twelfth aspect of the present disclosure provides a method for performing channel estimation of a first channel for a wireless communication between a receiver and a transmitter. The method comprises: transmitting, by the transmitter, a wireless signal to the receiver via the first channel; receiving, by the receiver, the wireless signal from the transmitter via the first channel; and estimating, by the receiver, an attenuation of an amplitude of the received wireless signal. The method further comprises: transmitting, by the receiver, the estimated attenuation of the amplitude of the received wireless signal to the transmitter via a second channel; receiving, by the transmitter, the estimated attenuation from the receiver via the second channel; and estimating, by the transmitter, a phase change between a phase of the wireless signal received by the receiver and a phase of the wireless signal transmitted by the transmitter, based on the estimated attenuation.

A thirteenth aspect of the present disclosure provides a system comprising a transmitter and a receiver, wherein the transmitter and receiver are configured to perform the method according to the twelfth aspect. A fourteenth aspect of the present disclosure provides a portable device comprising a receiver according to the first aspect or any of its implementation forms.

The portable device may be a headset, in particular a headset for virtual reality, e.g. virtual reality gaming.

The system of the eleventh aspect, the method of the twelfth aspect, the system of the thirteenth aspect and the portable device of the fourteenth aspect each achieve the same advantages as the receiver of the first aspect and its respective implementation forms and respective optional features as well as the same advantages as the transmitter of the third aspect and its respective implementation forms and respective optional features.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

Figure 1 shows an example of a receiver according to the first aspect of the present disclosure and an example of a transmitter according to the third aspect of the present disclosure;

Figure 2A shows a transmitter according to an embodiment of the present disclosure;

Figure 2B shows a receiver according to an embodiment of the present disclosure; Figure 3 shows a transmitter according to an embodiment of the present disclosure and a receiver according to an embodiment of the present disclosure; Figure 4 shows a transmitter according to an embodiment of the present disclosure and a receiver according to an embodiment of the present disclosure;

Figure 5 shows wireless signals according to an embodiment of the present disclosure; and

Figure 6 shows an example of a method according to the second aspect of the present disclosure and an example of a method according to the fourth aspect of the present disclosure. In the following, corresponding elements are labelled by the same reference sign. The term

“wireless signal” may be referred to in short as “signal”.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows an example of a receiver 2 according to the first aspect of the present disclosure and an example of a transmitter 1 according to the third aspect of the present disclosure.

The transmitter 1 of Figure 1 is a transmitter for wireless communication with a receiver, such as the receiver 2. The transmitter 1 is configured to transmit a wireless signal to the receiver 2 via a first channel CHI (this is indicated in Figure 1 by a corresponding dashed arrow). The transmitter 1 is configured to receive channel estimation information from the receiver 2 via a second channel CH2 (this is indicated in Figure 1 by a corresponding dashed arrow). The channel estimation information comprises an estimated attenuation of an amplitude of the wireless signal. The transmitter 1 is further configured to estimate a phase change between a phase of the wireless signal received by the receiver 2 and a phase of the wireless signal transmitted by the transmitter 1, based on the estimated attenuation of the amplitude of the wireless signal. For a detailed description of implementation forms of the transmitter 1 of Figure 1 reference is made to the above description with regard to the transmitter of the third aspect of the present disclosure as well as to the following description with regard to Figures 2 A and 3 to 6.

The receiver 2 is a receiver for wireless communication with a transmitter, such as the transmitter 1. The receiver 2 is configured to receive a wireless signal from the transmitter 1 via the first channel CHI and determine channel estimation information by estimating an attenuation of an amplitude of the received wireless signal. The receiver 2 is further configured to transmit the channel estimation information to the transmitter 1 via the second channel CH2, wherein the channel estimation information comprises the estimated attenuation of the amplitude of the received wireless signal without information on a phase change between a phase of the received wireless signal and a phase of the wireless signal transmitted by the transmitter 1.

For a detailed description of implementation forms of the receiver 2 of Figure 1, reference is made to the above description with regard to the receiver of the first aspect of the present disclosure as well as to the following description with regard to Figures 2B and 3 to 6.

The above description of a first channel and a second channel with regard to the receiver of the first aspect and the transmitter of the third aspect is correspondingly valid for the first channel CHI and the second channel CH2.

Figure 2A shows a transmitter 1 according to an embodiment of the present disclosure.

The transmitter of Figure 2A corresponds to the transmitter 1 of Figure 1. Therefore, the above description of the transmitter 1 of Figure 1 is valid for describing the transmitter 1 of Figure 2A and in the following an implementation form of the transmitter of Figure 1 according to an embodiment of the present disclosure is described.

As shown in Figure 2A, the transmitter 1 may comprise a communication circuitry la and a processing circuitry lb which are configured to perform, conduct or initiate the various operations of the transmitter 1 described herein. The communication circuitry la may comprise or correspond to at least one communication unit, in particular at least one communication module. The processing circuitry lb may comprise or correspond to at least one processing unit, in particular at least one processing module.

In particular, the communication circuitry la may be configured to transmit a wireless signal to the receiver 2 via the first channel CHI (not shown in Figure 2A) and to receive a wireless signal from the receiver 2 via the second channel CH2 (not shown in Figure 2A). In other words, the communication circuitry la may be configured for wireless communication, e.g. based on respectively using millimeter electromagnetic waves. Thus, the communication circuitry la may be configured to transmit data, e.g. one or more data frames, respectively information in the form of one or more wireless signals (may be referred to as one or more wireless data signals) to the receiver 2 via the first channel CHI. The communication circuitry la may be configured to transmit a wireless training signal having an initial amplitude known by the receiver 2 to the receiver 2 via the first channel CHI. This may allow the receiver 2 to estimate the attenuation (by the first channel CHI) of the amplitude of the wireless training signal as a result of the wireless training signal propagating via the first channel CHI. The communication circuitry la may be configured to receive data respectively information, e.g. channel estimation information, from the receiver 2 via the second channel CH2. The communication circuitry la may be configured to be controlled by the processing circuitry lb.

In particular, the processing circuitry lb may be configured to estimate a phase change between a phase of the wireless signal received by the receiver 2 and a phase of the wireless signal transmitted by the transmitter 1, based on the estimated attenuation of the amplitude of the wireless signal. The estimated attenuation of the amplitude of the wireless signal may be received by the transmitter 1 via the communication circuitry la, in particular as part of channel estimation information, from the receiver 2 via the second channel CH2. The processing circuitry lb may be configured to control the communication circuitry la, in particular the wireless communication performable by the communication circuitry la.

The communication circuitry la may comprise hardware and/or the communication circuitry la may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The hardware may comprise one or more antennas for wireless communication. In particular, the hardware may comprise one or more antennas for wireless communication with the receiver 2 via the first channel CHI and via the second channel CH2. The processing circuitry lb may comprise hardware and/or the processing circuitry lb may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise or correspond to components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The hardware of the processing circuitry lb may comprise two local oscillators (LO), a power amplifier (PA) and/or one or a low noise amplifier (LNA). In particular, the hardware of the processing circuitry lb may comprise a first LO and a PA so that the communication circuitry la may transmit a wireless signal to the receiver 2 via the first channel CHI. The hardware of the processing circuitry lb may comprise a second LO and a LNA for processing a wireless signal received by the communication circuitry l from the receiver 2 via the second channel CH2.

The transmitter 1 may further comprise memory circuitry (not shown in Figure 2A), which stores one or more instruction(s) that can be executed by the processing circuitry lb and optionally the communication circuitry la, in particular under control of the respective software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processing circuitry lb and optionally the communication unit la, causes the various operations of the transmitter 1 to be performed.

In one embodiment, the processing circuitry lb of the transmitter 1 comprises one or more processors and a non-transitory memory connected to the one or more processors. The non- transitory memory may carry executable program code which, when executed by the one or more processors, causes the transmitter 1 to perform, conduct or initiate the operations or methods described herein.

The above description regarding a wireless communication between the transmitter 1 and the receiver 2 is only by way of example for describing the function of the transmitter 1. Therefore, the above description is also valid for a wireless communication between the transmitter 1 and any other receiver.

Figure 2B shows a receiver 2 according to an embodiment of the present disclosure. The receiver 2 of Figure 2B corresponds to the receiver of Figure 1. Therefore, the above description of the receiver 2 of Figure 1 is valid for describing the receiver of Figure 2B and in the following an implementation form of the receiver 2 of Figure 1 according to an embodiment of the present disclosure is described.

As shown in Figure 2B, the receiver 2 may comprise a communication circuitry 2a and a processing circuitry 2b which are configured to perform, conduct or initiate the various operations of the receiver 2 described herein. The communication circuitry 2a may comprise or correspond to at least one communication unit, in particular at least one communication module. The processing circuitry 2b may comprise or correspond to at least one processing unit, in particular at least one processing module.

In particular, the communication circuitry 2a may be configured to receive a wireless signal from the transmitter 1 via the first channel CHI (not shown in Figure 2B) and to transmit the channel estimation information (in particular in form of a wireless signal) to the transmitter 1 via the second channel CH2 (not shown in Figure 2B). In other words, the communication circuitry 2a may be configured for wireless communication, e.g. based on respectively using millimeter electromagnetic waves. In particular, the communication circuitry 2a may be configured to receive data, e g. one or more data frames, respectively information in the form of one or more wireless signals (may be referred to as one or more wireless data signals) from the transmitter 1 via the first channel CHI. The communication circuitry 2a may be configured to receive a wireless training signal having an initial amplitude known by the receiver 2 from the transmitter 1 via the first channel CHI. This allows the receiver 2, in particular the processing circuitry 2b, to estimate the attenuation (by the first channel CHI) of the amplitude of the wireless training signal as a result of the wireless training signal propagating via the first channel CHI. The communication circuitry 2a may be configured to transmit data respectively information, e.g. channel estimation information, to the transmitter 1 via the second channel CH2. The communication circuitry 2a may be configured to be controlled by the processing circuitry 2b.

In particular, the processing circuitry 2b may be configured to determine channel estimation information by estimating an attenuation of an amplitude of a received wireless signal (received by the communication circuitry 2a), wherein the channel estimation information comprises the estimated attenuation of the amplitude of the received wireless signal without information on a phase change between a phase of the received wireless signal and a phase of the wireless signal transmitted by the transmitter 1. The processing circuitry 2b may be configured to control the communication circuitry 2a, in particular the wireless communication performable by the communication circuitry 2a.

The communication circuitry 2a may comprise hardware and/or the communication circuitry 2a may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The hardware may comprise one or more antennas for wireless communication. In particular, the hardware may comprise one or more antennas for wireless communication with the transmitter 1 via the first channel CHI and via the second channel CH2.

The processing circuitry 2b may comprise hardware and/or the processing circuitry 2b may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise or correspond to components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The hardware may comprise a local oscillator (LO), a power amplifier (PA) and/or a low noise amplifier (LNA). In particular, the hardware of the processing circuitry 2b may comprise a LNA for processing a wireless signal received by the communication circuitry 2a from the transmitter 1 via the first channel CHI. The hardware of the processing circuitry 2b may comprise a LO and a PA so that the communication circuitry 2a may transmit a wireless signal to the transmitter 1 via the second channel CH2. Since the receiver 2, in particular the processing circuitry 2b, does not estimate the phase change between the phase of the wireless signal received by the receiver 2 and the phase of the wireless signal transmitted by the transmitter 1, the processing circuitry 2b does not comprise a LO for processing the wireless signal received by the communication circuitry 2a from the transmitter 1 via the first channel CHI. In other words, the receiver does not comprise a LO for channel estimation of the first channel. That is, the receiver 2 is a receiver without a local oscillator for channel estimation of the first channel, in particular estimation of the phase change.

The receiver 2 may further comprise memory circuitry (not shown in Figure 2B), which stores one or more instruction(s) that can be executed by the processing circuitry 2b and optionally the communication circuitry 2a, in particular under control of the respective software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processing circuitry 2b and optionally the communication unit 2a, causes the various operations of the receiver 2 to be performed.

In one embodiment, the processing circuitry 2b of the receiver 2 comprises one or more processors and a non-transitory memory connected to the one or more processors. The non- transitory memory may carry executable program code which, when executed by the one or more processors, causes the receiver 2 to perform, conduct or initiate the operations or methods described herein.

The above description regarding a wireless communication between the receiver 2 and the transmitter 1 is only by way of example for describing the function of the receiver 2. Therefore, the above description is also valid for a wireless communication between the receiver 2 and any other transmitter.

Figure 3 shows a transmitter 1 according to an embodiment of the present disclosure and a receiver 2 according to an embodiment of the present disclosure.

In particular, Figure 3 shows functional blocks of the receiver and the transmitter 1 for describing the function of the transmitter 1 and the receiver 2 according to an embodiment of the present disclosure. The transmitter 1 of Figure 3 corresponds to the transmitter 1 of Figure 2A and the receiver 2 of Figure 3 corresponds to the receiver 2 of Figure 2B. Therefore, the above description with regard to the transmitter 1 of Figures 1 and 2A is valid for describing the transmitter 1 of Figure 3 and the above description with regard to the receiver 2 of Figures 1 and 2B is valid for describing the receiver 2 of Figure 3.

As shown in Figure 3, the transmitter 1 is configured to receive channel estimation information from the receiver 2 via the second channel CH2 (cf. functional block 11 of Figure 3). The channel estimation information comprises an estimated attenuation of an amplitude of a wireless signal, wherein the transmitter 1 transmitted the wireless signal to the receiver 2 via the first channel CHI. That is, the estimated attenuation of the amplitude of the wireless signal corresponds to the attenuation by the first channel CHI, when the wireless signal propagates via the first channel CHI. The transmitter 1 is configured to estimate a phase change between the phase of the wireless signal received by the receiver 2 and the phase of the wireless signal transmitted by the transmitter 1, based on the estimated attenuation of the amplitude of the wireless signal (cf. functional block 12 of Figure 3).

The transmitter 1 may be configured to perform precoding, in particular time reversal precoding, based on the estimated phase change and the received estimated attenuation (cf. functional block 13 of Figure 3). That is, the transmitter 1 may be configured to apply, based on the estimated phase change and the received estimated attenuation, precoding to data before transmitting the data in the form of a wireless signal to the receiver 2 via the first channel CHI . This achieves focusing of the wireless signal, transmitted by the transmitter 1, to the receiver 2 via the first channel CHI . In particular, due to the precoding temporal and spatial wave-focusing may be achieved.

The transmitter 1 may be configured to perform amplitude modulation for generating the wireless signal. Thus, the data comprised by the wireless signal may be modulated on the amplitude of the wireless signal (cf. functional block 14 of Figure 3). The transmitter 1 is configured to transmit a wireless signal to the receiver 2 via the first channel CHI (cf. functional block 15 of Figure 3). Said wireless signal may optionally comprise precoded, e.g. time reversal precoded, data (cf. functional block 13 of Figure 3) and/or may optionally be generated by amplitude modulation (cf. functional block 14 of Figure 3).

As shown in Figure 3, the receiver 2 is configured to receive a wireless signal from the transmitter 1 via the first channel CHI (cf. functional block 21 of Figure 3). The wireless signal may be a wireless training signal having an initial amplitude known by the receiver 2.

The receiver 3 may be configured to detect the amplitude of the received wireless signal for estimating an attenuation of the amplitude of the received wireless signal (cf. functional block 22 of Figure 3). The receiver 2 may comprise an amplitude detector for detecting the amplitude of the received wireless signal. The amplitude detector may be an envelope detector. The receiver 2 is configured to determine channel estimation information by estimating the attenuation of the amplitude of the received wireless signal (cf. functional block 23 of Figure 3), wherein the channel estimation information comprises the estimated attenuation of the amplitude of the received wireless signal without information on a phase change between a phase of the received wireless signal and a phase of the wireless signal transmitted by the transmitter. That is, with regard to estimating the effects of the first channel CHI, namely attenuation effect and phase change effect, on a wireless signal propagating via the first channel CHI, the receiver 2 is configured to only estimate the attenuation effect of the first channel CHI on the wireless signal.

The receiver 2 is further configured to transmit the channel estimation information to the transmitter 1 via the second channel CH2 (cf. functional block 24 of Figure 3). This allows providing feedback on the first channel CHI, in the form of the estimated attenuation of the wireless signal received by the receiver 2, to the transmitter 1 via the second channel CH2. Due to this feedback the transmitter may estimate the effect of the first channel CHI on the phase of the wireless signal propagating via the first channel CHI. That is, the transmitter is configured to estimate the phase change between the phase of the wireless signal received by the receiver 2 and the phase of the wireless signal transmitted by the transmitter 1, based on the estimated attenuation of the amplitude of the wireless signal. As soon as the transmitter 1 knows the effects by the first channel CHI on a wireless signal propagating via the first channel CHI, the transmitter may perform precoding, in particular time-reversal precoding, for compensating these channel effects of the first channel CHI and, thus achieving a temporal and spatial wave focusing of a wireless signal to the receiver 2 when transmitting the wireless signal. In other words, the transmitter 1 may perform the precoding based on the estimated phase change and the received estimated attenuation.

Figure 4 shows a transmitter 1 according to an embodiment of the present disclosure and a receiver 2 according to an embodiment of the present disclosure.

The transmitter 1 of Figure 4 corresponds to the transmitter 1 of Figure 3 and the receiver 2 of Figure 4 corresponds to the receiver 2 of Figure 3. Therefore, the above description with regard to the transmitter 1 of Figures 1, 2A and 3 is valid for describing the transmitter 1 of Figure 4 and the above description with regard to the receiver 2 of Figures 1, 2B and 3 is valid for describing the receiver 2 of Figure 4.

For the following description, it is assumed that the transmitter 1 transmits a wireless training signal to the receiver 2 via the first channel CHI, wherein the training signal has an initial amplitude known by the receiver 2. As shown in Figure 4, the receiver 2 may comprise an antenna 44 for receiving the training signal from the transmitter 1 via the first channel CHI. The receiver 2 may comprise a low noise amplifier (LNA) 43 for amplifying the amplitude (may be referred to as signal level) of the received training signal without significantly degrading its signal-to-noise ratio (SNR). The receiver 2 may comprise an envelope detector (ED) 45 for detecting the amplitude of the received training signal. The receiver 2 may comprise another type of amplitude detector.

As indicated by the functional block 23 of Figure 4, the receiver 2 may be configured to estimate the attenuation of the amplitude of the received training signal as follows: The receiver 2 may be configured to compute a difference between the amplitude of the received training signal and the initial amplitude of the training signal to estimate the attenuation of the amplitude of the received wireless training signal. In particular, the receiver 2 may be configured to compute, in the frequency domain, the difference between the amplitude of the received training signal and the initial amplitude of the training signal to generate an absolute value of a frequency response (abs(H)) of the first channel CHI. Therefore, the channel estimation information may comprise the absolute value of the frequency response of the first channel CHI as an indicator of the estimated attenuation of the amplitude of the received wireless signal. The receiver 2 may use respectively perform at least one Fourier Transform (FT), in particular at least one Fast Fourier Transform (FFT), for the computation in the frequency domain.

In particular, the receiver 2 may be configured to estimate the attenuation of the amplitude of the received wireless signal by estimating, for two or more sub-bands of the first channel, the attenuation of the amplitude of the received wireless signal.

The receiver 2 may comprise a local oscillator (LO) 42 and a power amplifier (PA) 41 for transmitting the channel estimation information in the form of a wireless signal to the transmitter 1 via the second channel CH2. The receiver 2 may comprise an antenna 44 for transmitting the channel estimation information, in the form of the wireless signal, to the transmitter 1 via the second channel CH2. The channel estimation information comprises the estimated attenuation of the amplitude of the received wireless signal (in particular in form of the absolute value of the frequency response of the first channel CHI) without information on a phase change between a phase of the received wireless signal and a phase of the wireless signal transmitted by the transmitter 1. Optionally, the antenna 44 for receiving a signal from the transmitter 1 via the first channel CHI and the antenna 44 for transmitting a signal to the transmitter 1 via the second channel CH2 may correspond to each other or may be part of a common antenna arrangement.

As shown in Figure 4, the transmitter 1 may comprise an antenna 44 for transmitting a wireless signal, such as a wireless data signal comprising a data frame or a wireless training signal having an initial amplitude known by the receiver 2, to the receiver 2 via the first channel CHI. The transmitter 1 may comprise an antenna 44 for receiving a wireless signal comprising the channel estimation information, determined by the receiver 2, from the receiver 2 via the second channel CH2. Optionally, the antenna 44 for transmitting a signal to the receiver 2 via the first channel CHI and the antenna 44 for receiving a signal from the receiver 2 via the second channel CH2 may correspond to each other or may be part of a common antenna arrangement.

The transmitter 1 may comprise a low noise amplifier (LNA) 43 for amplifying the amplitude of the received wireless signal without significantly degrading its SNR. The transmitter 1 may comprise a local oscillator (LO) 42 for processing the received wireless signal.

As indicated by the functional block 12 of Figure 4, the transmitter 1 may be configured to estimate the phase change between the phase of the training signal received by the receiver 2 and the phase of the training signal transmitted by the transmitter 1, based on the estimated attenuation of the amplitude of the training signal by performing one or more phase reconstruction algorithms based on the estimated attenuation. The one or more phase reconstruction algorithms comprise at least one of one or more sparse algorithms and one or more Griffin-Lim algorithms.

In particular, the transmitter 1 is configured to receive the channel estimation information comprising the absolute value of the frequency response of the first channel CHI as an indicator of the estimated attenuation from the receiver 2 via the second channel CH2. In this case, the transmitter 2 may perform, in the frequency domain, the one or more phase reconstruction algorithms based on the absolute value of the frequency response of the first channel to estimate the phase change.

As indicated by the functional blocks 13 of Figure 4, the transmitter 1 may be configured to perform time reversal (h(-t)*) precoding based on the estimate attenuation of the amplitude of the training signal (received from the receiver 2) and the estimated phase change between the phase of the training signal received by the receiver 2 and the phase of the training signal transmitted by the transmitter 1. In particular, the transmitter 1 may be configured to apply, based on the estimated phase change and the received estimated attenuation, time reversal precoding to data before transmitting the data in the form of a wireless signal to the receiver 2 via the first channel CHI.

The transmitter 1 may comprise an amplitude modulator (AM) 46 for amplitude modulation to generate a wireless signal. Thus, for transmitting data in the form of a wireless signal (wireless data signal) the transmitter 1 may be configured to modulate the data on the amplitude of the wireless signal. The receiver 2 may comprise a local oscillator (LO) 42 and a power amplifier (PA) 41 for transmitting a wireless signal, in particular pre-coded data in the form of a wireless signal generated by amplitude modulation, to the receiver 2 via the second channel CHI. The transmitter 1 may comprise an antenna 44 for transmitting the wireless signal to the receiver 2 via the first channel CHI.

As can be seen in Figure 4, at the receiver side, there is no IQ modulation or demodulation. Furthermore, at the receiver side, there is no local oscillator (LO) for receiving a wireless signal from the transmitter 1 via the first channel CHI. A simple amplitude detection, such as an envelope detection using an envelope detector (ED) 45, is sufficient at the receiver 2 for both data detection and providing to the transmitter 1 a feedback on the attenuation effect of the first channel CHI.

Since the estimation of the phase change effect of the first channel CHI, i.e. the phase change estimation, is performed at the transmitter side, the complexity of the receiver 2, in particular of the processing circuitry of the receiver 2, is reduced.

In particular, for each sub-band of the first channel CHI the attenuation of the amplitude of the receive signal may be estimated by the receiver 2 and sent back to the transmitter 1 via the second channel CH2 using a simple feedback scheme.

At the transmitter side, using the optimization algorithm of equation (1), a matrix F may be determined, wherein the matrix F is a matrix of exponential of the delays for each path of multi paths M and each sub-band of the sub-bands K of the first channel CHI. As outlined above, multi-paths may occur in case the wireless communication via the first channel CHI is an indoor communication. M is the number of paths, which is assumed to be known and K is the number of sub-bands of the first channel CHI. Therefore, the size of the matrix F may be M X K . min H I H| ² — |F * A| ² || (1)

In the above question (1), H is the vector of computed channel impulse responses for each sub band of the K sub-bands of the first channel CHI (size l x K) and A is the vector of amplitudes of the different M paths (size M x l).

The phase recovery technique proposed herein is based on that the transmitter 1 knows the absolute value of the frequency response of the first channel CHI . For this the receiver 2 may be configured to transmit to the transmitter 1 via the second channel CH2 the absolute value of the frequency response of the first channel CHI, in particular for each sub-band of the first channel CHI. In particular, the receiver 2 may be configured to compute, in the frequency domain, the absolute value of the Fast Fourier Transform (FFT) of the first channel CHI as the absolute value of the frequency response of the first channel CHI. This is shown in the following equation (2): abs(H) = abs(FFT(r_x)/FFT(t_x)) (2)

In equation (2), abs(H) corresponds to the absolute value of the frequency response of the first channel CHI. The frequency response of the first channel CHI may also be referred to as channel response of the first channel CHI in the frequency domain. In equation (2), tx corresponds to a training signal transmitted by the transmitter 1 and rx correspond to the training signal received by the receiver 2, wherein the training signal has an initial amplitude known by the receiver 2. With regard to the channel estimation information, the estimated absolute value of the frequency response of the first channel CHI may be the only parameter that is transmitted from the receiver 2 to the transmitter 1 via the second channel as a feedback on the effects of the first channel CHI. The feedback from the receiver 2 to the transmitter 1 via the second channel CH2 may be done in a lower frequency band compared to the wireless communication via the first channel CHI for simplicity of the receiver side. In particular, the local oscillator (LO) 42 of the transmitter 1 and the local oscillator (LO) 42 of the receiver 2 used for wireless communication via the second channel CH2 may each be a sub 6GHz local oscillator. In particular, the wireless communication from the receiver 2 to the transmitter 1 via the second channel CH2 may have a lower data rate compared to the data rate of the wireless communication from the transmitter

1 to the receiver 2 via the first channel CHI .

The transmitter 1 may apply a phase reconstruction algorithm on the received estimated absolute value of the frequency response of the first channel CHI. The phase reconstruction algorithm may be a Griffin-Lim Algorithm (GLA). This algorithm is able to reconstruct the signal using the amplitude of the Gabor Transform (DGT) of the signal. This transform is a short time Fourier Transform of a signal. Since the first channel CHI is considered to be stationary, this time frequency transform is equivalent to a Fast Fourier Transform (FFT) or a Discrete Fourier Transform (DFT). As outlined already above the GLA is only one possible example of a phase reconstruction algorithm and, thus, any other type of phase reconstruction algorithm may be used for estimating the phase change between the phase of the training signal transmitted by the transmitter 1 and the phase of the training signal received by the receiver 2.

Figure 5 shows wireless signals according to an embodiment of the present disclosure.

In particular Figure 5 shows wireless signals that may be transmitted by a transmitter 1 according to any one of Figures 1, 2A, 3 and 4, and that may received by a receiver 2 according to any one of Figures 1, 2B, 3 and 4. Therefore, in the following reference is made to the transmitter 1, receiver 2, first channel CHI and second channel CH2 of Figures 1 to 4.

The transmitter 1 may be configured to transmit a data frame to the receiver 2 via the first channel CHI by transmitting a wireless data signal 52a, 52b comprising the data frame and a wireless training signal 51 a, 51 b to the receiver 2 via the first channel CHI , wherein the receiver

2 knows the initial amplitude of the training signal. Transmitting a training signal before a data signal, e.g. the training signal 51a before the data signal 52a respectively the training signal 51b before the data signal 52b, allows the receiver 2 to provide the estimated attenuation of the training signal as feedback to the transmitter 1 via the second channel CH2. As a result, the transmitter 1 may perform channel estimation of the first channel CHI by estimating the phase change of the phase of the training signal transmitted by the transmitter 1 and the phase of the training signal received by the receiver 2 based on the received estimated attenuation of the amplitude of the training signal. As a result, the transmitter 1 gets to know the effects of the first channel on the amplitude of the training signal (attenuation) and on the phase of the training signal (phase change) when the training signal propagates via the first channel CHI . This allows the transmitter 1 to perform time reversal precoding on the data of the data frame so that the data signal, e.g. data signal 52 a or 52b, is focused by the transmitter 1 to the receiver 2, when the data signal is transmitted from the transmitter 1 to the receiver 2 via the first channel CHI .

In case the receiver 2 is part of a portable device, i.e. the receiver side may be mobile, the first channel CHI may change over time. This change of the first channel CHI is mostly due to human body movements of a person using the portable device, which may be considered as a slow movement compared to the data rate of the wireless communication via the first channel CHI. This issue may be solved by the above description of transmitting a wireless data signal in combination with a wireless training signal. That is, the transmitter 1 may be configured to transmit data frames based on a training signal that is inserted into the beginning and/or the end of each data frame. Since the transmitter 1 and receiver 2 may be configured to wirelessly communicate at a very high symbol rate using some GHz bandwidth respectively millimeter electromagnetic waves, the speed of the channel estimation update performed by the transmitter 1 based on the estimated attenuation, received from the receiver 2, of the amplitude of a training signal is greater than the changing time of the first channel CHI. In particular, the transmitter

1 and receiver 2 may be used for a short-range communication, which means that the round trip delay of the wireless signal between the transmitter 1 and the receiver 2 may be very short. Thus, the channel estimation update performed by the transmitter 1 based on the estimated attenuation, received from the receiver 2, of the amplitude of a training signal is much faster than the channel changing period of the first channel CHI .

Figure 6 shows an example of a method according to the second aspect of the present disclosure and an example of a method according to the fourth aspect of the present disclosure.

As shown in Figure 6, a method for operating a transmitter (e.g. the transmitter 1 of Figures 1 to 5) may comprise the step S61 a of transmitting a wireless signal to a receiver (e.g. the receiver

2 of Figures 1 to 5) via a first channel and the step S62a of receiving channel estimation information from the receiver via a second channel. The channel estimation information comprises an estimated attenuation of an amplitude of the wireless signal. The method may further comprise the step S63a of estimating a phase change between a phase of the wireless signal received by the receiver and a phase of the wireless signal transmitted by the transmitter, based on the estimated attenuation of the amplitude of the wireless signal.

Further, as shown in Figure 6, a method for operating a receiver (e.g. the receiver 2 of Figures 1 to 5) may comprise the step S61b of receiving a wireless signal from a transmitter (e.g. the transmitter 1 of Figures 1 to 5) via a first channel and the step S62b of determining channel estimation information by estimating an attenuation of an amplitude of the received wireless signal. The method may further comprise the step S63b of transmitting the channel estimation information to the transmitter via a second channel, wherein the channel estimation information comprises the estimated attenuation of the amplitude of the received wireless signal without information on a phase change between a phase of the received wireless signal and a phase of the wireless signal transmitted by the transmitter.

For a detailed description of implementation forms of the methods of Figure 6, reference is made to the above description of the method of the second aspect of the present disclosure and the method of the fourth aspect of the present disclosure as well as to the above description with regard to Figures 1 to 5.

The transmitter 1 and receiver 2 of the present disclosure may achieve the following advantages: No local oscillator and IQ modulator are required at the receiver side for a channel estimation. This reduces the complexity, size, weight, and power consumption of the receiver. With regard to the channel estimation, at the receiver side, merely an attenuation of the amplitude of a received wireless signal is estimated for determining channel estimation information and, thus, the channel estimation complexity is reduced at the receiver side. Since the estimation of the phase change of the phase of a wireless signal transmitted by the transmitter and the phase of the wireless signal received by the receiver is performed at the transmitter side and, thus, not at the receiver side, there is no need of a carrier frequency recovery at the receiver side. A simple envelope detector at the receiver side is sufficient for recovering the amplitude of a received wireless signal, in particular modulated signal, without the need of a carrier offset recovery or compensation techniques and algorithms. For the reasons outlined above, the power consumption at the receiver side is significantly reduced. A time reversal pre-coding at the transmitter side allows to achieve temporal and spatial wave-focusing for transmitting wireless signals from the transmitter to the receiver via the first channel.

The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed subject matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.