WO2023065122A1

WO2023065122A1 - Channel state information error compensation

Info

Publication number: WO2023065122A1
Application number: PCT/CN2021/124765
Authority: WO
Inventors: Wenjian Wang; Xiagang XU; Fei Gao
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2021-10-19
Filing date: 2021-10-19
Publication date: 2023-04-27
Also published as: CN118120278A

Abstract

Embodiments of the present disclosure relate to device, method, apparatus and computer readable storage media of CSI error compensation. The method comprises: transmitting, at a first device and based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain; upon receipt of a second signal for sensing on the compound channel, determining an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and performing amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters. The I/Q imbalance compensation scheme can achieve accurate sensing CSI by utilizing the pilot pattern with less overhead and non-linear compensation. By this way, the performance, stability and the transmit signal pattern of the communication system can be improved.

Description

CHANNEL STATE INFORMATION ERROR COMPENSATION

FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication and in particular to devices, methods, apparatuses and computer readable storage media of channel state information (CSI) error compensation.

BACKGROUND

There is a growing interest in joint communication and sensing system (JCAS) . In the JCAS system, JCAS devices, such as, base stations and UEs, can communicate with each other, and simultaneously sense the environment to determine locations and speeds of nearby objects. A wide variety of emerging applications rely on accurate measurements of CSI obtained from JCAS devices. A time series of the CSI measurements reflect how wireless signals travel through surrounding objects and humans in time, frequency, and spatial domains, so they can be used for various wireless sensing applications. For example, CSI amplitude variations in the time domain have different patterns for different humans, activities, gestures, and so on, which can be used for human presence detection, fall detection, motion detection, activity recognition, gesture recognition, and human identification/authentication. CSI phase shifts in the spatial and frequency domains, i.e., in the transmit/receive antennas and carrier frequencies, are related to signal transmission delay and direction, which can be used for human localization and tracking. CSI phase shifts in the time domain may have different dominant frequency components, which can be used for estimation of breathing rate of human.

SUMMARY

Example embodiments of the present disclosure provide a solution of CSI error compensation.

In a first aspect, there is provided a first device. The first device comprises at least one processor; and at least one memory including computer program codes; the at least one memory and the computer program codes are configured to, with the at least one processor, cause the first device at least to: transmit, based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain; upon receipt of a second signal for sensing on the compound channel, determine an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and perform amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.

In a second aspect, there is provided a method. The method comprises: transmitting, at a first device and based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain; upon receipt of a second signal for sensing on the compound channel, determining an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and performing amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.

In a third aspect, there is provided an apparatus. The apparatus comprises: means for transmitting, based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain; means for upon receipt of a second signal for sensing on the compound channel, determining an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and means for performing amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.

In a fourth aspect, there is provided a computer readable medium having a computer program stored thereon which, when executed by at least one processor of a device, causes the device to carry out the method according to the second aspect.

Other features and advantages of the embodiments of the present disclosure will also be apparent from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure are presented in the sense of examples and their advantages are explained in greater detail below, with reference to the accompanying drawings, where

FIG. 1 illustrates an example network environment in which example embodiments of the present disclosure can be implemented;

FIG. 2 illustrates a flowchart of an example method of CSI error compensation according to some example embodiments of the present disclosure;

FIG. 3 illustrates a schematic diagram of a pilot signal pattern for CSI error compensation according to some example embodiments of the present disclosure;

FIGs. 4A and 4B illustrate a schematic diagram of amplitudes of received odd and even subcarriers based on the pilot signal pattern for CSI error compensation according to some example embodiments of the present disclosure;

FIG. 5 illustrates a schematic diagram of performance evaluations based on various compensation schemes according to some example embodiments of the present disclosure;

FIG. 6 shows a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

FIG. 7 shows a block diagram of an example computer readable medium in accordance with some embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an example embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish functionalities of various elements. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as fifth generation (5G) systems, Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Narrow Band Internet of Things (NB-IoT) , Wi-Fi and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the future fifth generation (5G) new radio (NR) communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR Next Generation NodeB (gNB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology. A RAN split architecture comprises a gNB-CU (Centralized unit, hosting RRC, SDAP and PDCP) controlling a plurality of gNB-DUs (Distributed unit, hosting RLC, MAC and PHY) . A relay node may correspond to DU part of the IAB node.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE) , a subscriber station (SS) , a portable subscriber station, a mobile station (MS) , or an access terminal (AT) . The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (e.g., remote surgery) , an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. The terminal device may also correspond to Mobile Termination (MT) part of the integrated access and backhaul (IAB) node (a. k. a. a relay node) . In the following description, the terms “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

Although functionalities described herein can be performed, in various example embodiments, in a fixed and/or a wireless network node, in other example embodiments, functionalities may be implemented in a user equipment apparatus (such as a cell phone or tablet computer or laptop computer or desktop computer or mobile IoT device or fixed IoT device) . This user equipment apparatus can, for example, be furnished with corresponding capabilities as described in connection with the fixed and/or the wireless network node (s) , as appropriate. The user equipment apparatus may be the user equipment and/or or a control device, such as a chipset or processor, configured to control the user equipment when installed therein. Examples of such functionalities include the bootstrapping server function and/or the home subscriber server, which may be implemented in the user equipment apparatus by providing the user equipment apparatus with software configured to cause the user equipment apparatus to perform from the point of view of these functions/nodes.

An integrated JCAS or 5G NR system has attracted much attention, since it has advantages in reducing the system size, weight, and power consumption, mitigating electromagnetic interferences, and a multitude of scenarios of application. Different sensing applications may vary from requirements of signal processing techniques and classification/estimation algorithms. Some CSI measurement error sources could be summarized as follows:

1) power amplifier uncertainty (PAU) , which may be due to the resolution limitation of hardware, for example, 0.5 dB for Atheros 9380, the total gain achieved from LNA and PGA cannot perfectly compensate the signal amplitude attenuation to the transmitted power level; the measured CSI amplitude equals to the compensated power level, mixed with a power amplifier uncertainty error, which causes a CSI amplitude offset;

2) I/Q imbalance, which may be caused when the amplitude and phase distortion occurs and the orthogonal baseband signal will be destroyed; once the I/Q is imbalanced, after sampling and FFT, the result will be a deformed CSI;

3) carrier frequency offset (CFO) : the central frequencies of a transmission pair may not be perfectly synchronized; the carrier frequency offset is compensated by the CFO corrector of the receiver, but due to the hardware imperfection, the compensation may be incomplete, and signal still carries residual CFO, which leads to a time-varying CSI phase offset across subcarriers;

4) sampling frequency offset (SFO) : the sampling frequencies of the transmitter and the receiver exhibit an offset due to non-synchronized clocks, which can cause the received signal after ADC a time shift with respect to the transmitted signal; after the SFO corrector, residual SFO leads to a rotation error; because clock offsets are relatively stable within a short time (e.g., in the order of minutes [10] ) , such phase rotation errors are nearly constant;

5) packet detection delay (PDD) , which stems from energy detection or correlation detection which occurs in digital processing after down conversion and ADC sampling; packet detection introduces another time shift phase rotation error;

6) PLL phase offset (PPO) , which is responsible for generating the center frequency for the transmitter and the receiver, starting at random initial phase; as a result, the CSI phase measurement at the receiver may be corrupted by an additional phase offset;

7) phase ambiguity (PA) : when examining the phase difference between two receive antennas, recent work validates a so called four-way phase ambiguity existence when working on 2.4 GHz.

Among them, I/Q imbalance has a most significant impact on the JCAS system due to non-linear errors. Such errors are common in various sensing devices and communication perception systems, which results in inaccurate CSI. The inaccurate CSI may in turn impact subsequent signals from the transmitter device to the receiver device in the JCAS and have a great impact on the performance of the JCAS. The traditional systems obtain a relatively better sensing CSI performance at the cost of system resources. Typically, I/Q imbalance is removed with high complexity technologies or complicated algorithms, for example, the maximum likelihood (ML) estimation and the expectation maximization (EM) algorithm. The differential filter is also used for I/Q imbalance estimation. However, a large number of pilot symbols are required in these methods, and thus the computation complexity is considerably high, and it is a waste of system resources. Hence, it is necessary to improve the system performance in terms of the non-linear error processing and CSI accuracy with a low computation complexity.

FIG. 1 illustrates an example network environment 100 in which example embodiments of the present disclosure can be implemented. The network environment 100 may be a JCAS system or any other network system mmWave massive MIMO. For example, the system 100 may be a device free JCAS system of BC with mono-static sensing.

As shown in FIG. 1, the example environment 100 may comprise a plurality of devices including a first device 110 (hereinafter which may be also referred to as the base station (BS) 110 or gNB 110) and a second device 120 (hereinafter which may be also referred to as the UE 120) . The example environment 100 also includes at least one object.

In the environment 100, the first device 110 and the second device 120 perform point-to-point (P2P) communications, and simultaneously sense the environment to determine parameters or characteristics of nearby objects (e.g., the object 102) , which includes, but not limited to, locations, speeds, gestures, activities, identities of nearby objects, and the like. There are multi-path channels between the first device 110 and the second device 120. In the context of the present disclosure, the multi-path channels may be also referred to as a compound channels. A link from the first device 110 to the second device 120 is referred to as a downlink (DL) , while a link from the second device 120 to the first device 110 is referred to as an uplink (UL) .

It is assumed that the first device 110 has N transmit antennas and the second device 120 has N receive antennas, . Thus, there are N×N pairs of transmit and receive antennas in total, and the first device 110 and the second device 120 communicate packets or signals through the N×N antenna array.

The first device 110 may directly transmit packets or signals for communication with the second device 120. Additionally, or alternatively, the first device 110 may also transmit packets or signals for sensing. As shown in FIG. 1, the signals transmitted from the first device 110 may propagate along a compound channel. Once meeting the object 102, the signals for sensing will be reflected by the object 102, and then arrive at and received by the first device 110.

The first device 110 may generate CSI for the compound channel based on the received signal for sensing. With the CSI, the first device 110 may adjust or further refine the transmit signal pattern, so as to maximize the mutual information (MI) between the compound channel and the reflected signal from the object to be sensed at the first device 110.

A packet transmitted by the first device 110 may include data payload, together with a pilot signal for synchronization and channel estimation. There are various forms of pilot signals, including a comb-type pilot, a block-type pilot, a Lattice-type pilot, etc. Without loss of generality, in the context of embodiments of the present disclosure, a general data structure comprises a sequence of training symbols, denoted by L _t, and data symbols, denoted by L _d, for each spatial stream. Thus, the total length of the sensing signal is denoted by L=L _t+L _d. By concatenating the symbols from N spatial streams into a matrix X, the signal transmitted from the second device 120 to the first device 110 may be denoted by X= [X _t, X _d] , where

and

with X _t (n) and X _d (n) denoting the pilot symbols and data symbols transmitted from the n-th antenna, respectively.

In practice, assuming that a frequency-flat Rayleigh fading channel is between the first device 110 and the second device 120. The first device 110 measures and analyzes the signals for sensing, and estimates the compound channel between the first device 110 and the second device 120. In particular, the signal for sensing may be reflected by the object 102 and received at the first device 110 with I/Q imbalance and CFO, which can be expressed as below:

where Δand φ denote amplitude and phase mismatches respectively, andy (t) denotes the baseband received signal.

In the example embodiments, the baseband received signal y (t) can be determined as below:

where h and τ denote the complex channel gain and the time delay, respectively. n (t) denotes the additive Gaussian noise process with a single side-band power spectrum of N ₀, and x (t) denotes the transmitted baseband OFDM signal for sensing.

In the example embodiments, the transmitted baseband OFDM signal x (t) can be determined as below:

where N _d and N _p denote the number of data and pilot symbols, respectively. T _s denotes the sampling time, T denotes the OFDM symbol length, N is the total number of subcarriers, S denotes the average transmitting power, g (t) detnoes the transmission pulse, respectively. d (k, i) denotes the k-th subcarrier of the i-th modulated symbol.

In the example embodiments, after applying FFT operation on the equation (3) , the received signal in frequency domain can be determined as:

In the presence of I/Q imbalance and CFO, the subcarriers are interfered by frequency mirror-image subcarriers, i.e., inter carrier interference (ICI) . The ICI will lead to the channel impulse response (CIR) degradation. Here, S (l-k) is defined as the complex coefficient for the ICI components between l-th and k-th subcarriers, which can be expressed as below:

where ε denotes the normalized frequency offset.

|S (l-k) | indicates that the weight of the desired signal component S (0) decreases whereas the undesired weights of the ICI components increase for a larger ε. Note that the adjacent subcarrier has the maximum contribution to the ICI.

To reduce the effect of I/Q imbalance and ICI due to CFO, there is provided an improved channel estimation and compensation method with low computation complexity and high CSI accuracy.

It is to be understood that the number of the first device, the second device, and the object is given for the purpose of illustration without suggesting any limitations to the present disclosure. The network system 100 may include any suitable number of devices and/or object adapted for implementing implementations of the present disclosure, and the compound channel between the first device and the second device may be more complex or simple. Although not shown, it would be appreciated that one or more additional devices may be located in the environment 100.

It should be also understood that, although illustrated as a base station and a terminal device, the first device 110 and the second device 120 may be other devices or a part of the base station and the terminal device, for example, at least a part of a terrestrial network device or a non-terrestrial network device.

Depending on the communication technologies, the network system 100 may be a Code Division Multiple Access (CDMA) network, a Time Division Multiple Address (TDMA) network, a Frequency Division Multiple Access (FDMA) network, an Orthogonal Frequency-Division Multiple Access (OFDMA) network, a Single Carrier-Frequency Division Multiple Access (SC-FDMA) network or any other. Communications discussed in the network 100 may conform to any suitable standards including, but not limited to, New Radio Access (NR) , Long Term Evolution (LTE) , LTE-Evolution, LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , Code Division Multiple Access (CDMA) , cdma2000, and Global System for Mobile Communications (GSM) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) , a future sixth generation communication protocols. The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, certain aspects of the techniques are described below for NR and JCAS in the description below.

Principle and implementations of the present disclosure will be described in detail below with reference to FIGs. 2 to 5. FIG. 2 illustrates a flowchart of an example method 200 of CSI error compensation according to some example embodiments of the present disclosure. For the purpose of discussion, the process 200 will be described with reference to FIG. 1. The process 200 may involve the first device 110, the second device 120 and the object 102.

At 210, the first device 110 transmits, based on a pilot pattern, a first signal on the compound channel. As discussed above, the subcarriers are interfered by frequency mirror-image subcarriers, that is, the adjacent subcarrier has the most contribution to the ICI. Thus, an enhanced pilot pattern is used to effectively separate the desired signals and the mirror-image signals in the example embodiments of the present disclosure. The enhanced pilot signal can be defined as below:

According to the definition in equation (7) , the first signal transmitted by the first device 110 may include a set of pilot symbols set to a first value (e.g., 1) and a second value (e.g., 0) interleaved on a group of subcarriers in frequency domain. The set of pilot symbols starts with the first value on the group of subcarriers.

FIG. 3 illustrates a schematic diagram of a pilot signal pattern for CSI error compensation according to some example embodiments of the present disclosure. As shown in FIG. 3, according to a conventional pilot pattern, the pilot symbols almost fill the subcarrier in frequency domain, and thus more network resources are used. Compared with the pilot pattern, the pilot symbols set to the value “1” and the value “0” are interleaved on the subcarriers in frequency domain, and thus less network resources are used.

At 220, the first device 110 receives a second signal for sensing on the compound channel. The second signal is produced by reflecting the first signal by the object 102 on the compound channel.

At 230, the first device 110 determines an amplitude and phase mismatch parameter based on the second signal and the pilot pattern. To determine amplitude and phase mismatch parametersΔand φ, and to achieve the accurate compensation with a small number of pilot symbols, an operator R (k) is derived based on (5) , as below:

As a result, the amplitude and phase mismatch parameters Δand φ can be determined as below:

In other words, the real component of R (k) represents the amplitude mismatch, and the imaginary component of R (k) represents the phase mismatch.

At 240, the first device 110 performs amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.

To minimize the impact of the inter-subcarrier interference, the even subcarriers may be selected for pair averaging. This is because the adjacent subcarrier has contributed larger interference into the k-th subcarrier compared to other subcarriers. FIGs. 4A and 4B illustrate a schematic diagram of amplitudes of received odd and even subcarriers based on the pilot signal pattern for CSI error compensation according to some example embodiments of the present disclosure.

In some example embodiments, by performing the amplitude and phase compensation, the first device 110 may derive a target signal from the second signal. The first device 110 may then determine the CSI for the compound channel based on the target signal. Since I/Q imbalance and CFO are compensated, the CSI determined from the target signal is more accurate than the CSI determined directly from the received second signal. As a result, the compound channel can be more accurately characterized by the CSI.

Assuming that the noise power and the phase mismatch φ are small and thus can be ignored, I/Q imbalance compensation is to implement in time domain can be determined as below:

where

denotes the compensated received signal in time domain, that is, the target signal.

In some example embodiments, the first device 110 may determine a transmit signal pattern based on the CSI, so as to maximize the MI between the compound channel and the received signal that is reflected from the object.

In some example embodiments, the first device 110 may transmit a third signal on the compound channel based on the transmit signal pattern. The first device 110 may then receive a fourth signal for sensing which is reflected by the object 102 on the compound channel. Since the third signal is transmitted based on the refined transmit signal pattern, the first device 110 may derive the MI between the compound channel and the fourth signal, as below:

where Ξ is derived based on the compensated compound channel

Θ denotes a preconfigured matrix that satisfies Θ ^HΘ=I _N,

denotes the right unitary matrix after singular value decomposition (SVD) of the compound channel covariance matrix

and Λ=diag ( [λ _1, 1, ..., λ _i, i, ..., λ _N, N) denotes a diagonal matrix with λ _i, i being the singular values.

In some example embodiments, the first device 110 may perform the entire or only a part of the process 200 for more than one time, so as to constantly adjust its channel model and the transmit signal pattern, and to derive the accurate CSI. By way of example, in a case that the object 102 moves and thus its position changes, additionally or alternatively the state of the compound channel changes, the terminal device and the network device may need to implement the process 100 again.

Although the first device 110 is given as the actor of the method 200, it should be understood that, the compensation scheme and the proposed pilot pattern are also applicable to the terminal devices, such as, the second device 120. The present disclosure is not limited in this regard.

It should be understood that the formulas, equations, expressions, algorithms, etc. described in method 200 are given for illustrative purpose without any limitations. The PHE compensation scheme, especially the compensation information, may be in a different form or implemented by using variations of what is described above.

According to the example embodiments of the present disclosure, there is provided an improved CSI compensation scheme. In the proposed compensation scheme, an enhanced pilot pattern is designed to effectively separate the desired signal from the mirror-image signal with less power consumption. Thus, the accuracy of CSI can be improved, which in turn facilitates the optimization of the transmit signal pattern. In addition, non-linear channel compensation can be realized with a low computation complexity and overhead, thus t the performance, stability and the transmit signal pattern of the communication system can be improved.

FIG. 5 illustrates a schematic diagram for performance evaluations in various cases according to some example embodiments of the present disclosure. The performance evaluations shown in FIG. 5 are obtained based on the simulation parameters shown in Table 1 below.

Table 1. simulation parameters for CSI error compensation scheme

As shown in FIG. 5, the yellow line denotes the simulation result obtained in a conventional case where I/Q imbalance and CFO exist, and no CSI compensation is performed; the blue line denotes the simulation result obtained in the conventional case where I/Q imbalance and CFO exist, and CFO compensation is performed, but no I/Q imbalance compensation is performed; the red line denotes the simulation result obtained in a conventional case where I/Q imbalance and CFO exist, and I/Q imbalance compensation is performed, but no CFO compensation is performed; the green line denotes the simulation result obtained in an ideal case where no I/Q imbalance and CFO exist; and the pink line denotes the simulation result obtained in a case where I/Q imbalance and CFO exist, and both CSI compensation and CFO compensation are performed based on the scheme proposed in the present disclosure. Compared with the conventional case, by adopting the proposed scheme, a nearly similar performance to the system without any CFO and I/Q imbalance influences can be achieved.

In some example embodiments, an apparatus capable of performing the method 200 (for example, implemented at the first device 110 or the second device 120) may comprise means for performing the respective steps of the method 200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for transmitting, based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain; means for upon receipt of a second signal for sensing on the compound channel, determining an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and means for performing amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.

In some example embodiments, the first value is 1 and the second value is 0, and the set of pilot symbols starts with the first value on the group of subcarriers.

In some example embodiments, the apparatus further comprises means for obtaining a target signal in time domain by performing the amplitude and phase compensation on the second signal.

In some example embodiments, the apparatus comprises: means for determining channel state information, CSI, for the compound channel based on the target signal; means for determining a transmit signal pattern based on the channel state information; means for transmitting, based on the transmit signal pattern, a third signal on the compound channel; and means for receiving a fourth signal for sensing on the compound channel, the signal being produced by reflecting the third signal by at least one object on the compound channel.

In some example embodiments, the means for determining the transmit signal pattern comprises: means for determining the transmit signal pattern such that mutual information, MI, between the compound channel and the fourth signal is maximized. The compound channel is characterized by the CSI determined based on the target signal.

In some example embodiments, the means for determining the amplitude and phase parameter comprises: means for, for each even indexed subcarrier of the group of subcarriers, determining a pair averaging mismatch parameter based on the second signal and the pilot pattern; means for determining a real component of the pair averaging mismatch parameter as an amplitude mismatch parameter of the second signal; and means for determining an imaginary component of the pair averaging mismatch parameter as a phase mismatch parameter of the second signal.

In some example embodiments, the apparatus comprises one of a network device or a terminal device.

FIG. 6 is a simplified block diagram of a device 600 that is suitable for implementing embodiments of the present disclosure. The device 600 may be provided to implement the communication device, for example the first device 110 and the second device 120 as shown in FIG. 1. As shown, the device 600 includes one or more processors 610, one or more memories 620 coupled to the processor 610, and one or more transmitters and/or receivers (TX/RX) 640 coupled to the processor 610.

The TX/RX 640 may be configured for bidirectional communications. The TX/RX 640 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

The processor 610 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 600 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 620 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 624, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , and other magnetic storage and/or optical storage media. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 622 and other volatile memories that will not last in the power-down duration.

A computer program 630 includes computer executable instructions that may be executed by the associated processor 610. The program 630 may be stored in the ROM 624. The processor 610 may perform any suitable actions and processing by loading the program 630 into the RAM 622.

The embodiments of the present disclosure may be implemented by means of the program 630 so that the device 600 may perform any process of the disclosure as discussed with reference to FIG. 2. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some embodiments, the program 630 may be tangibly contained in a computer readable medium which may be included in the device 600 (such as in the memory 620) or other storage devices that are accessible by the device 600. The device 600 may load the program 630 from the computer readable medium to the RAM 622 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. FIG. 7. shows an example of the computer readable medium 700 in form of CD or DVD. The computer readable medium has the program 630 stored thereon.

Various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations. It is to be understood that the block, device, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the method 200 as described above with reference to FIG. 2. Generally, program modules may include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing device, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, device or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A first device comprising:

at least one processor; and

at least one memory including computer program codes;

the at least one memory and the computer program codes are configured to, with the at least one processor, cause the first device at least to:

transmit, based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain;

upon receipt of a second signal for sensing on the compound channel, determine an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and

perform amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.
The first device of Claim 1, wherein the first value is 1 and the second value is 0, and the set of pilot symbols starts with the first value on the group of subcarriers.
The first device of Claim 1, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to:

obtain a target signal in time domain by performing the amplitude and phase compensation on the second signal.
The first device of Claim 3, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to:

determine channel state information, CSI, for the compound channel based on the target signal;

determine a transmit signal pattern based on the CSI;

transmit, based on the transmit signal pattern, a third signal on the compound channel; and

receive a fourth signal for sensing on the compound channel, the fourth signal being produced by reflecting the third signal by at least one object on the compound channel.
The first device of Claim 4, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to determine the transmit signal pattern by:

determining the transmit signal pattern such that mutual information, MI, between the compound channel and the fourth signal is maximized, the compound channel being characterized by the CSI determined based on the target signal.
The first device of Claim 1, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to determine the amplitude and phase parameter by:

for each even indexed subcarrier of the group of subcarriers, determining a pair averaging mismatch parameter based on the second signal and the pilot pattern;

determining a real component of the pair averaging mismatch parameter as an amplitude mismatch parameter of the second signal; and

determining an imaginary component of the pair averaging mismatch parameter as a phase mismatch parameter of the second signal.
The first device of Claim 1, wherein the first device comprises one of a network device or a terminal device.
A method comprising:

transmitting, at a first device and based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain;

upon receipt of a second signal for sensing on the compound channel, determining an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and

performing amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.
The method of Claim 8, wherein the first value is 1 and the second value is 0, and the set of pilot symbols starts with the first value on the group of subcarriers.
The method of Claim 8, further comprising:

obtaining a target signal in time domain by performing the amplitude and phase compensation on the second signal.
The method of Claim 10, further comprising:

determining channel state information, CSI, for the compound channel based on the target signal;

determining a transmit signal pattern based on the CSI;

transmitting, based on the transmit signal pattern, a third signal on the compound channel; and

receiving a fourth signal for sensing on the compound channel, the signal being produced by reflecting the third signal by at least one object on the compound channel.
The method of Claim 11, wherein determining the transmit signal pattern comprises:

determining the transmit signal pattern such that mutual information, MI, between the compound channel and the fourth signal is maximized, the compound channel being characterized by the CSI determined based on the target signal.
The method of Claim 8, wherein determining the amplitude and phase parameter comprises:

for each even indexed subcarrier of the group of subcarriers, determining a pair averaging mismatch parameter based on the second signal and the pilot pattern;

determining a real component of the pair averaging mismatch parameter as an amplitude mismatch parameter of the second signal; and

determining an imaginary component of the pair averaging mismatch parameter as a phase mismatch parameter of the second signal.
The method of Claim 8, wherein the first device comprises one of a network device or a terminal device.
An apparatus comprising:

means for transmitting, based on a pilot pattern, a first signal on a compound channel, the first signal comprising a set of pilot symbols set to a first value and a second value interleaved on a group of subcarriers in frequency domain;

means for upon receipt of a second signal for sensing on the compound channel, determining an amplitude and phase mismatch parameter based on the second signal and the pilot pattern, the second signal being produced by reflecting the first signal by at least one object on the compound channel; and

means for performing amplitude and phase compensation on the second signal based on the amplitude and phase mismatch parameters.
A computer readable medium comprising program instructions for causing an apparatus to perform at least the method of any of Claims 8 to 14.