Reference signal designs

Abstract

Example embodiments of the present disclosure are directed to enable channel estimation using reference signals, symbols, or pilot designs A method comprises determining a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix; and transmitting, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

Description

REFERENCE SIGNAL DESIGNS CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from, and the benefit of, Finland Application No.20245545, filed May 2, 2024, which is hereby incorporated by reference in its entirety. FIELD

[0002] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for enabling channel estimation using reference signals, symbols, or pilot designs. BACKGROUND

[0003] To technical evolutions in Artificial Intelligence (AI) and Machine Learning (ML) start to impact the wireless standardization for Physical Layer (PHY). The 3GPP discussion focuses on potential enhancement for accurate positioning, Channel State Information (CSI) feedback and beam management with the help of AI / ML. Among these technical challenges, precise channel knowledge plays an important role, where the channel needs to be explicitly estimated / predicted by means of AI / ML or inherently estimated / predicted in conjunction with corresponding AI / ML-based feature or functionality. SUMMARY

[0004] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: determine a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix; and transmit, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

[0005] In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: receive, from a first apparatus, at least one reference sequence determined at least partly based on a parametrization of a non-orthogonal code matrix and information identifying the at least one reference sequence; and perform an estimation on at least one channel between the first apparatus and the second apparatus at least partially based on a post-coding operation performed on the at least one reference sequence.

[0006] In a third aspect of the present disclosure, there is provided a method. The method comprises: determining a plurality of reference sequences at least partly based on a parametrization of a non- orthogonal code matrix; and transmitting, to a second apparatus, at least one reference sequencefrom the plurality of reference sequences and information identifying the at least one reference sequence.

[0007] In a fourth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a first apparatus, at least one reference sequence determined at least partly based on a parametrization of a non-orthogonal code matrix and information identifying the at least one reference sequence; and performing an estimation on at least one channel between the first apparatus and the second apparatus at least partially based on a post-coding operation performed on the at least one reference sequence.

[0008] In a fifth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for determining a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix; and means for transmitting, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

[0009] In a sixth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for receiving, from a first apparatus, at least one reference sequence determined at least partly based on a parametrization of a non-orthogonal code matrix and information identifying the at least one reference sequence; and means for performing an estimation on at least one channel between the first apparatus and the second apparatus at least partially based on a post- coding operation performed on the at least one reference sequence.

[0010] In a seventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the third aspect.

[0011] In an eighth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourth aspect.

[0012] It is to be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0014] FIG.1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0015] FIG.2 illustrate a signaling chart for communication according to some example embodimentsof the present disclosure;

[0016] FIG.3 illustrates an example of channel estimation for non-orthogonal ABBA code according to some example embodiments of the present disclosure;

[0017] FIGS.4A and 4B illustrate examples of time domain use case and frequency domain use case according to some example embodiments of the present disclosure, respectively;

[0018] FIG. 5 illustrates an example process reflecting the solution according to some example embodiments of the present disclosure;

[0019] FIG.6 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0020] FIG.7 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0021] FIG.8 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0022] FIG.9 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0023] Throughout the drawings, the same or similar reference numerals represent the same or similar element. DETAILED DESCRIPTION

[0024] 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. Embodiments described herein can be implemented in various manners other than the ones described below.

[0025] 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.

[0026] 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 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.

[0027] It shall be understood that although the terms “first,” “second,”…, etc. in front of noun(s) andthe like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0028] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0029] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0030] 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.

[0031] 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.

[0032] 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 ahardware 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.

[0033] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), 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) 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 fifth generation (5G), 5.5G, the sixth generation (6G) 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.

[0034] 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), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0035] 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), portablecomputers, 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 a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0036] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0037] FIG.1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. As shown in FIG.1, the communication network 100 may comprise a first apparatus 110 which may be a transmitter, for example, a terminal device. In some example embodiments, the terminal device may also be discussed as a UE.

[0038] The communication network 100 may further comprise a second apparatus 120, which may be a receiver, for example, a network device. In some example embodiments, the network device may be discussed as a BS, a gNB, or an eNB.

[0039] A serving area provided by the second apparatus 120 is called a cell. The first apparatus 110 may communicate with the second apparatus 120 within the cell 102. The cell currently serving the first apparatus 110 may be considered as a serving cell 102.

[0040] In the following, for the purpose of illustration, some example embodiments are described with the first apparatus 110 operating as a terminal device and the second apparatus 120 operating as a network device. However, in some example embodiments, operations described in connection with a terminal device may be implemented at a network device or other device, and operations described in connection with a network device may be implemented at a terminal device or other device.

[0041] In some example embodiments, if the first apparatus 110 is a terminal device and second apparatus 120 is a network device, a link from the second apparatus 120 to the first apparatus 110 is referred to as a downlink (DL), while a link from the first apparatus 110 to the second apparatus 120 is referred to as an uplink (UL). In DL, the second apparatus 120 is a transmitting (TX) apparatus (or a transmitter) and the first apparatus 110 is a receiving (RX) apparatus (or a receiver). In UL, the first apparatus 110 is a TX apparatus (or a transmitter) and the second apparatus 120 is a RX apparatus (or a receiver).

[0042] It is to be understood that the number of network devices and terminal devices shown in FIG.1 is given for the purpose of illustration without suggesting any limitations. The communication environment 100 may include any suitable number of network devices and terminal devices.

[0043] Communications in the communication network 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), 5.5G, the sixth generation (6G), and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple- Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0044] As described, potential enhancement for accurate positioning, Channel State Information (CSI) feedback and beam management with the help of AI / ML may be considered. On one side, the AI / ML- based estimation and prediction part can leap the performance in a complementary way. On the other side, it is necessary to re-think / re-design, if advanced pilot or reference symbol design can better facilitate both AI / ML-based and conventional channel estimation. Moreover, in a wireless system, there may be also interfering transmissions whose influence needs to be accounted for. Thus, it is typically not even possible to select orthogonal sequences for all transmissions, but it may often be a tradeoff between availability of orthogonal resources and interference tolerance, also for channel estimation use cases.

[0045] In this situation, a creation of a set of non-orthogonal pilot / reference sequences is desired. These should exhibit performance advantages in channel estimation with orthogonal / unitary pilot design It is noted that orthogonal / unitary designs often have these features only in limited circumstances (e.g. at a transmitter), and their design may not be optimal, since estimation is carriedout in the receivers under various imperfections and network models that each affect interference and estimation performance.

[0046] In accordance with some example embodiments of the present disclosure, there is provided a solution for pilot / reference design. In this solution, the first apparatus 110 determines a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix and transmit, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

[0047] In this way, multiple channels can be estimated by the observations of at least one receive antenna. The proposed solution may be extensible to easily support the system with both low-order and high-order antenna configuration. The multiple channels may be formed e.g. by multiple different radio patterns, that be by implemented by using different beams of subsets thereof, different antennas or subsets thereof, different transmission sectors, different transmission panels (e.g. at UE), as so on.

[0048] Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0049] Reference is now made to FIG. 2, which shows a signaling chart 200 for communication according to some example embodiments of the present disclosure. As shown in FIG.2, the signaling chart 200 involves a first apparatus 110 and a second apparatus 120. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 200. In some example scenarios associated with the signaling chart 200, the first apparatus 110 may act as a transmitter and the second apparatus 120 may act as a receiver.

[0050] Although a first apparatus 110 and a single second apparatus 120 are illustrated in FIG.2, it would be appreciated that there may be a plurality of first apparatuses and a plurality of second apparatuses performing similar operations as described with respect to the first apparatus 110 and the second apparatus 120 below, respectively.

[0051] As shown in FIG. 2, the first apparatus 110 may generate (205) a plurality of reference sequences, which may be considered as any type of reference signal used in the communication network. For example, the first apparatus 110 may generate the plurality of reference sequences associated with a plurality of pilot sequences and corresponding transmit power levels.

[0052] For generating the plurality of reference sequences, for example, for 4×4 scheme, e.g., 4×4 transmit-receive antenna structure, two 2×2 mother code matrices may be introduced, namely ^^^^^^^^and ^^^^^^^^, which are represented as below, respectively:where ^^^^^^^^ and ^^^^^^^^ denote a complex pilot and the corresponding transmit power level for ^^^^ = 1,2,3,4.

[0053] A non-orthogonal code matrix may be used for generating the reference sequences based on the mother code matrices ^^^^^^^^and ^^^^^^^^. The mother code matrices ^^^^^^^^and ^^^^^^^^herein used may be 2×2 orthogonal mother code matrix. It is to be understood that some non-orthogonal or quasi- orthogonal mother code matrices may also be applied for the mother code matrices.

[0054] Furthermore, the non-orthogonal code matrix used herein for generating the reference sequences may be a non-orthogonal ABBA code matrix. It is to be understood that any other suitable non-orthogonal code matrix. For example, the non-orthogonal ABBA code may be extensible for a2^^^^ × 2^^^^ STC system with ^^^^ = 2,3,4 …, based on fundamentally an arbitrary 2 × 2 unitary matrix.

[0055] As an example, the plurality of pilot sequences as mentioned above may be generated by a seed pilot sequence. The seed pilot sequence may comprise at least one of a Chadoff-Zhu sequence, a Gold sequence, or a Kasami sequence, etc.

[0056] As an example, by using the non-orthogonal ABBA code matrix, the reference sequences can be constructed based on mother code matrices ^^^^^^^^and ^^^^^^^^. The generated reference signal may be represented as:

[0057] At each = , sequence , , , betransmitted in a certain order, defined by ABBA code matrix ^^^^4, through space domain. For example, at time instance t1, the transmission order of pilot sequence ^^^^1, ^^^^2, ^^^^3, and ^^^^4through space domain may follow the first row in the matrix shown in Equation (3), namely ^^^^1, ^^^^2, ^^^^3, and ^^^^4, and at time instance t2, the transmission order of pilot sequence ^^^^1, ^^^^2, ^^^^3, and ^^^^4through space domain may follow the second row in the matrix shown in Equation (3), namely ^^^^2, ^^^^1, ^^^^4and ^^^^3.

[0058] The plurality of pilot sequences ^^^^1, ^^^^2, ^^^^3, and ^^^^4may comprise one of a Chadoff-Zhu sequence, a Gold sequence, or a Kasami sequence, where a corresponding seed ^^^^seedis needed to explicitly generate a pilot sequence. Additionally, a seed ^^^^seedis necessary to define the power pattern to allocate the power levelfor the pilot symbol ^^^^^^^^. For successfully detection, the seed information of ^^^^seedand ^^^^seedis consistently required both at the transmitter and the receiver.

[0059] As mentioned above, reference sequences may be generated by a parameterization of a non- orthogonal code matrix, e.g., the non-orthogonal ABBA code matrix.

[0060] In addition, or alternatively, a pre-coding operation may be performed on the generated reference sequences by using a pre-coding matrix. For 4×4 scheme, e.g., 4×4 transmit-receive antenna structure, a 4×4 pre-coding matrix in the spirit of diagonal-ABBA may be denoted as:where ^^^^2 is a 2 × 2 identity matrix.

[0061] That is, a pre-coded reference sequence(s) may be denoted as: ^^^^ = (^^^^4^^^^4)^^^^ + ^^^^ (5)where ^^^^ represents a reference channel characteristic of a channel between the first apparatus 110 and the second apparatus 120, and ^^^^ represents a reference noise.

[0062] Then the first apparatus 110 may transmit (210) the pre-coded reference sequence(s) to the second apparatus 120. Furthermore, the information identifying the reference sequence(s) may be provided to the receiver, such as the seed pilot sequence associated with the reference sequence(s), the power pattern associated with the reference sequence(s) and / or a subset of row / column of the non-orthogonal code matrix.

[0063] For example, information identifying the seed pilot sequences, and / or power patterns may be derived in one node (e.g. network) and indicated to another node (e.g. UE) via signaling channels. Moreover, a subset of columns and / or rows of a non-orthogonal code matrix may be assigned to a particular node. This may be indicated by appropriate index selection.

[0064] It is to be understood that that the matrix ^^^^4above may be transposed in that time runs horizontally and space vertically, without departing from the scope of the present disclosure. Non- orthogonal ABBA type matrix is an example of matrix where some columns are orthogonal to each other, while some interfere (or correlate) with at least one other.

[0065] At the second apparatus 120, upon receiving the pre-coded reference sequence(s), the second apparatus 120 may perform (215) a post-coding operation on the pre-coded reference sequence(s).

[0066] For example, at the second apparatus 120, after processed by a post-coding matrix ^^^^^4^^^, the post-coded reference signal may be denoted as:where ℎ1, ℎ2, ℎ3, and ℎ4represent respective channel characteristics of multiple channels between the first apparatus 110 and the second apparatus 120, ^�^^^1, ^�^^^2, ^�^^^3and ^�^^^4represent respective channel noises of the multiple channels, and ^^^^^4^^^is a transpose matrix of a pre-coding matrix for pre- coding the reference sequences, i.e., a 4×4 post-coding matrix.

[0067] To estimate the channel characteristics based on the pre-coded reference sequence(s), the second apparatus 120 may obtain an association between the reference sequences and the plurality of pilot sequences and the corresponding transmit power levels, which may also be considered as theinformation identifying the reference sequences, for example, joint code matrices denoted as:

[0068] Based on the joint code matrices and the post-coded reference signal listed above, the second apparatus 120 may perform (220) an estimation on at least one channel between the first apparatus 110 and the second apparatus 120.

[0069] For example, the channel can be estimated by:

[0070] That is, the second apparatus 120 may estimate the at least one channel by using a characteristic of a block-wise orthogonal matrix generated based on the post-coded reference signal (i.e., Equation (6)) and the association (i.e., Equations (7) and (8)).

[0071] The solution for pilot / reference signal design as described above may also be extended for other transmit-receive antenna structure, e.g., 8×8 transmit-receive antenna structure. It is noted that e.g.7x7 pilot design may be determined by a restriction of 8x8 design, e.g. by selection of a subset of columns / rows. In this situation, for generating the reference sequences, besides the mother code matrices listed by Equations (1) and (2), two further 2×2 mother code matrices may be introduced, namely ^^^^^^^^and ^^^^^^^^, which are represented as below, respectively: (11) (12)where ^^^^^^^^ and ^^^^^^^^ denote a complex pilot and the corresponding transmit power level for ^^^^ =1,2,3,4,5,6,7,8.

[0072] Similarly, the mother code matrices ^^^^^^^^and ^^^^^^^^herein used may be 2×2 orthogonal mother code matrix. It is to be understood that some non-orthogonal or quasi-orthogonal mother code matrices may also be applied for the mother code matrices.

[0073] A non-orthogonal code matrix, e.g., a non-orthogonal ABBA code matrix may be used for generating the reference sequences based on the mother code matrices ^^^^^^^^, ^^^^^^^^, ^^^^^^^^and ^^^^^^^^.

[0074] By using the non-orthogonal ABBA code matrix, the reference sequences can be constructed based on mother code matrices ^^^^^^^^, ^^^^^^^^, ^^^^^^^^and ^^^^^^^^. The generated reference signal may be represented as:^^^^ ^^^^ ^^^^ ^^^^

[0075] In addition, or alternatively, a pre-coding operation may be performed on the generated reference sequences by using a pre-coding matrix. For 8×8 scheme, e.g., 8×8 transmit-receive antenna structure, an 8×8 pre-coding matrix in the spirit of diagonal-ABBA may be denoted as:where ^^^^2 is a 2 × 2 identity matrix.

[0076] That is, a pre-coded reference sequence(s) may be denoted as: ^^^^ = (^^^^8^^^^8)^^^^ + ^^^^ (15)Where ^^^^ represents a reference channel characteristic of a channel between the first apparatus 110 and the second apparatus 120, and ^^^^ represents a reference noise.

[0077] At the second apparatus 120, upon receiving the pre-coded reference sequence(s), the second apparatus 120 may perform a post-coding operation on the pre-coded reference sequence(s).

[0078] For example, at the second apparatus 120, after processed by a post-coding matrix ^^^^^4^^^, the post-coded reference signal may be denoted as:

[0079] To estimate the channel characteristics based on the pre-coded reference sequence(s), the second apparatus 120 may obtain an association between the reference sequences and the plurality of pilot sequences and the corresponding transmit power levels, for example, joint code matrices denoted as: ^^^^8 = ^^^^^^^^ + ^^^^^^^^ + ^^^^^^^^ + ^^^^^^^^ (17)^^^^8 = ^^^^^^^^ − ^^^^^^^^ + ^^^^^^^^ − ^^^^^^^^ (18)^^^^8 = ^^^^^^^^ + ^^^^^^^^ − ^^^^^^^^ − ^^^^^^^^ (19)^^^^8 = ^^^^^^^^ − ^^^^^^^^ − ^^^^^^^^ + ^^^^^^^^ (20)

[0080] Similarly, channel estimation may be carried out as:

[0081] Consequently, the channel response can be block-wise estimated bywith ^^^^ = 2Re(^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^∗ ∗1 3 1 3 1 5 1 5 1 7 1 7 3 5 3 5 3 7 3 ^7 + ^^^^5^^^^7^^^^5^^^^7 +^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^^∗6 + ∗ ∗ ∗ ∗2 4 2 4 2 6 2 ^^^^2^^^^8^^^^2^^^^8 + ^^^^4^^^^6^^^^4^^^^6 + ^^^^4^^^^8^^^^4^^^^8 + ^^^^6^^^^8^^^^6^^^^8),ℎ�� 3� = 1Tr(^^^^^^^^^^^^ )⁄ 2with ^^^^ = 2Re(−^^^^ ^^^^ ^^^^ ^^^^∗3 + ^^^^ ^^^^ ^^ ∗ ∗ ∗ ∗ ∗1 3 1 1 5^^1^^^^5 − ^^^^1^^^^7^^^^1^^^^7 − ^^^^3^^^^5^^^^3^^^^5 + ^^^^3^^^^7^^^^3^^^^7 − ^^^^5^^^^7^^^^5^^^^7 −^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^^∗ − ^^^^ ^^^^ ^^^^ ^^^^∗ − ^^^^ ^^^^ ^^ ∗ ∗ ∗2 4 2 4 2 6 2 6 2 8 2 8 4 6^^4^^^^6 + ^^^^4^^^^8^^^^4^^^^8 − ^^^^6^^^^8^^^^6^^^^8),with ^^^^ = 2Re(^^^^ ∗ ∗ ∗ ∗ ∗ ∗1^^^^3^^^^1^^^^3 − ^^^^1^^^^5^^^^1^^^^5 − ^^^^1^^^^7^^^^1^^^^7 − ^^^^3^^^^5^^^^3^^^^5 − ^^^^3^^^^7^^^^3^^^^7 + ^^^^5^^^^7^^^^5^^^^7 +^^^^ ^^^^ ^^^^ ^^^^∗ − ^^^^ ^^^^ ^^^^ ^^∗ ∗ ∗ ∗ ∗2 4 2 4 2 6 2^^6 − ^^^^2^^^^8^^^^2^^^^8 − ^^^^4^^^^6^^^^4^^^^6 − ^^^^4^^^^8^^^^4^^^^8 + ^^^^6^^^^8^^^^6^^^^8),with ^^^^ = 2Re(−^^^^ ^^^^ ^^^^ ^^^^∗ − ^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^∗ ∗ ∗ ∗1 3 1 3 1 5 1 5 1 7 1 ^7 + ^^^^3^^^^5^^^^3^^^^5 − ^^^^3^^^^7^^^^3^^^^7 − ^^^^5^^^^7^^^^5^^^^7 −^^^^ ^^^^ ^^^^ ^^^^∗ − ^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^^∗ + ^^^^ ^^^^ ^^^^ ^^^^∗ − ^^^^ ^^^^ ^^^^ ^^^∗ ∗2 4 2 4 2 6 2 6 2 8 2 8 4 6 4 6 4 8 4 ^8 − ^^^^6^^^^8^^^^6^^^^8).

[0082] It is to be understood that the transmit power levels may be generalized so that they involve also complex phase. For example, the basic ABBA matrix has diversity order 2, but by incorporating appropriate phases the rank is 4. In some implementations, this effect can be obtained by selecting the pilot sequences appropriately. This selection depends on how the non-orthogonal matrix is constructed, e.g., which non-orthogonal code matrix is selected as a basis for pilot transmission.

[0083] Hereinafter, the advantages of the solution of present disclosure will be further described with reference to FIGS.3-5 and some simulation process.

[0084] In the numerical study, 1024-PSK may be deployed as the signal constellation for pilot symbols, in order to possibly reduce the chance of generating an ill-conditioned ABBA code matrix, even with random pilot selection for individual realization throughout the Monte Carlo simulation. As shown in FIG.3, the channel estimation quality, quantified by Normalized Mean Squared Error (NMSE), ispresented for the 4 × 4 and 8 × 8 ABBA code-based pilot sequences under independent andidentically distributed (i.i.d.) Rayleigh fading, in dependent of the Signal-to-Noise Ratio (SNR). Basically, the performance gain is a combination of the power gain and diversity gain.

[0085] FIGS.4A and 4B illustrate the user case of the proposed solution in time domain or in frequency domain, respectively. FIG.4A is applicable for low mobility scenarios, in which the channel can be assumed time-invariant during the time window of the four symbols. Similarly, if the channel can be assumed frequency-invariant for four neighboring subcarriers, the channel estimation can beprocessed, based on these adjacent subcarriers, as shown in FIG. 4B. Especially, FIG. 4B will be interested, because the Sounding Reference Signal (SRS)-based channel estimation is carried out by the frequency domain smoothing. The parameters shown in FIGS. 4A and 4B are described with respect to Equations (1)-(22), which will be omitted here.

[0086] In general, in the present disclosure, the non-orthogonal ABBA code may be extensible for a2^^^^ × 2^^^^ STC system with ^^^^ = 2,3,4 …, based on fundamentally an arbitrary 2 × 2 unitary matrix.

[0087] The power level coefficients ^^^^^^^^may help to create equivalently a Ring-QAM pilot constellation system, and significantly relax the random pilot selection to fulfill the full rank condition for the code matrices ^^^^^^^^to ^^^^^^^^.

[0088] Furthermore, the power level coefficients ^^^^^^^^may provide another degree of freedom to adjust the channel estimation quality for different streams, because the noise suppression factors, e.g. in(1a) and (b) as Re(^^^^ ∗ ∗1^^^^3^^^^1^^^^3 + ^^^^2^^^^4^^^^2^^^^4), can be constructively or de-constructively adjusted forindividual streams, according to the design purpose.

[0089] After exploiting the power level coefficients ^^^^^^^^, the per-stream channel estimation performance may be slightly imbalanced, nevertheless, the all-stream performance seems to be even better for theequal gain case with ^^^^^^^^ = 1, e.g. for 4 × 4 ABBA code.

[0090] The pilot pair(^^^^1,^^^^3)and / or(^^^^2,^^^^4)may be entangled to elimination the term Re(^^^^1^^^^3^^^^1^^^^3∗)and / or Re(^^^^2^^^^4^^^^ ∗2^^^^4) , by forcing Re(^^^^ ∗1^^^^3) = 0 and / or Re(^^^^ ∗2^^^^4) = 0 . Then, the channelestimation quality will be identically good for different streams, by introducing such rate ¾ or ½ pilot sequences. 1024-PSK may enable a large pool of pilot sequences and will whiten the pilot distribution.

[0091] In this way, multiple channels can be explicitly estimated by the observations of one receive antenna. Plenty of pilot sequences for selection, flexibility in code matrix construction and systematicextension toward a 2^^^^ × 2^^^^ non-orthogonal ABBA code.

[0092] Furthermore, low complexity can be reached to achieve power gain and diversity gain, e.g. two2 × 2-matrix-multiplication operations for the case exploiting 4 × 4 non-orthogonal ABBA code.

[0093] Last but not the least, the combination of 1024-PSK with the power level coefficients ^^^^^^^^poses the good approximate to shape Gaussian distributed pilot constellation, which is near optimal from information theoretic viewpoint.

[0094] The advantage of the proposed solution is that it is rich of candidate sequences. It is quite easy to create such Space-Time Code based pilot, which is very much relaxed, comparing to the OCC case with different constraints. For the sake of degree of freedom in code construction, based on the equations of the proposed 4x4 scheme. The second advantage of the proposed solution is that the power imbalanced pilots will empower the link adaptation functionality, which tunes the channel estimation quality from the instantaneous channel states and globally reach an equalized performance for different sub-channels.

[0095] The process shown in FIG.5 might be helpful to understand the additional diversity. As shown, the diversity gains through space time processing steps shown in FIG.5 is differently achieved by comparing to OCC.

[0096] Another aspect of the present disclosure is to be emphasized is that the code used in this solution individually is not orthogonal, but the pre-coding, post-coding and the STC feature pose diagonal-wise orthogonal pilots as a special case. This effect of “Orthogonality” out of “Non- Orthogonality” will bring in flexibility and create more sequences for the system in a manner of easy implementation. For the same reason, here symbol rate 1 code is used, but additional sequences would come from any code that has rate >1. As a matter of fact, the developing (even non-orthogonal) multi-sequence parametrization using some well-defined system enables mitigating interferences of these sequences (this is implicit in tx diversity of course, so using st- code framework is justified). In a large network, there are always non-orthogonal pilot sequences (just like there is always interference), at least from neighboring cells / beams / etc., but one idea here is to design those sequences from scratch so that the matrix X used for channel estimation in model y=Xh+n has good properties, as well easily parametrized (i.e., easily signalled).

[0097] Based on the solution of the present disclosure, the properties of space-time block code matrix constructions can be exploited to solve a technical problem, i.e., while in space-time code design the goal is to maximize performance (diversity order) when sending a given number of symbols, assuming the channel is known, here, the goal is to estimate as many channels as possible using a given number of symbols. Specifically, STC structure may be exploited for pilot / reference symbol sequences.

[0098] The parametrization of space-time matrices also enables efficient indication (signalling) for said sequences-for example, as mentioned above, a large number of suitable space-time reference symbol matrices may be generated by a seed symbol sequences, and the seed sequence may be, for example, even an existing sequence in 5G or other specification (e.g. Chadoff-Zhu, Gold sequence, Kasami sequence, etc with acceptable correlation properties).

[0099] At the receiver side, the spatial superimposed, but known pilots can be similarly resolved by the orthogonal STC code matrix, so that the channel can be accordingly estimated. Basically, following this principle, pilots can be constructed, for applying any art of STC codes with a unitary code matrix or with unitary basic matrices.

[0100] Without restricting the present disclosure, the ABBA non-orthogonal STC is used for the pilot construction as a particular enabling embodiment, whose STC code matrices are not unitary, i.e., they are on the whole non-orthogonal (although individual constituent matrices thereof may be unitary). With pre-coding and post-coding operations, the ABBA non-orthogonal code matrix can be transformed into a block-wise orthogonal matrix, so that transmit diversity can still be applied. This is illustrated in the following section. The advantage of applying the ABBA (or similar) non-orthogonalSTC is its flexibility to adapt to both low-order and high-order antenna configurations. Additionally, it also supports the imbalanced power allocation among the pilots under certain transmit power constraint, which will relieve the pilot contamination problem, without loss of channel estimation quality.

[0101] FIG. 6 shows a flowchart of an example method 600 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the first apparatus 110 in FIG.1.

[0102] At block 610, the first apparatus 110 determines a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix.

[0103] At block 620, the first apparatus 110 transmits, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

[0104] In some example embodiments, the non-orthogonal code matrix comprises a non-orthogonal ABBA code matrix.

[0105] In some example embodiments, the method 600 further comprises: generating a reference sequence based on a first 2×2 mother code matrix and a second 2×2 mother code matrix for 4×4 transmit-receive antenna structure, wherein the first 2×2 mother code matrix is associated with a first set of reference sequences and a first set of corresponding transmit power levels and the second 2×2 mother code matrix is associated with a second set of reference sequences and a second set of corresponding transmit power levels.

[0106] In some example embodiments, the method 600 further comprises: performing a precoding operation on the generated reference sequence by using a 4×4 precoding matrix constructed by a 2×2 identity matrix.

[0107] In some example embodiments, the method 600 further comprises: generating the reference sequence based on a first 2×2 mother code matrix, a second 2×2 mother code matrix, a third 2×2 mother code matrix and a fourth 2×2 mother code matrix for 8×8 transmit-receive antenna structure, wherein the first 2×2 mother code matrix is associated with a first set of reference sequences and a first set of corresponding transmit power levels, the second 2×2 mother code matrix is associated with a second set of reference sequences and a second set of corresponding transmit power levels, the third 2×2 mother code matrix is associated with a third set of reference sequences and a third set of corresponding transmit power levels and the fourth 2×2 mother code matrix is associated with a fourth set of reference sequences and a fourth set of corresponding transmit power levels.

[0108] In some example embodiments, the method 600 further comprises: performing a precoding operation on the generated reference sequence by using an 8×8 precoding matrix constructed by a 4×4 identity matrix.

[0109] In some example embodiments, the first, the second, the third or the fourth set of referencesequences is generated from a seed pilot sequence, and wherein the seed pilot sequence comprises at least one of a Chadoff-Zhu sequence, a Gold sequence, or a Kasami sequence.

[0110] In some example embodiments, the information identifying the at least one reference sequence comprises at least one of the following: a seed pilot sequence associated with the plurality of reference sequences, or a power pattern associated with the plurality of reference sequences, a subset of columns and / or rows of the non-orthogonal code matrix.

[0111] In some example embodiments, the first apparatus comprises a transmitter.

[0112] FIG.7 shows a flowchart of an example method 700 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 700 will be described from the perspective of the second apparatus 120 in FIG.1.

[0113] At block 710, the second apparatus 120 receives, from a first apparatus, at least one reference sequence that is at least partly non-orthogonal and information identifying the at least one reference sequence.

[0114] At block 720, the second apparatus 120 performs an estimation on at least one channel between the first apparatus and the second apparatus at least partially based on a post-coding operation performed on the at least one reference sequence.

[0115] In some example embodiments, the method 700 further comprises: performing the post-coding operation on the at least one reference sequence by using a post-coding matrix which is a transpose matrix of a pre-coding matrix for pre-coding the at least one reference sequence; and obtaining, from the information, an association between the at least one reference sequence and a plurality of reference sequences and corresponding transmit power levels; and estimating the at least one channel by using a characteristic of a block-wise orthogonal matrix generated based on at least one post-coded reference sequence and the association.

[0116] In some example embodiments, the 4×4 precoding matrix is constructed by a 2×2 identity matrix for 4×4 transmit-receive antenna structure.

[0117] In some example embodiments, the 8×8 precoding matrix is constructed by a 4×4 identity matrix for 8×8 transmit-receive antenna structure.

[0118] In some example embodiments, the information identifying the at least one reference sequence comprises at least one of the following: a seed pilot sequence associated with the plurality of reference sequences, or a power pattern associated with the plurality of reference sequences, a subset of columns and / or rows of the non-orthogonal code matrix.

[0119] In some example embodiments, the second apparatus comprises a receiver.

[0120] In some example embodiments, a first apparatus capable of performing any of the method 600 (for example, the first apparatus 110 in FIG.1) may comprise means for performing the respective operations of the method 600. The means may be implemented in any suitable form. For example, themeans may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG.1.

[0121] In some example embodiments, the first apparatus comprises means for determining a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix; and means for transmitting, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

[0122] In some example embodiments, the non-orthogonal code matrix comprises a non-orthogonal ABBA code matrix.

[0123] In some example embodiments, the first apparatus further comprises: means for generating a reference sequence based on a first 2×2 mother code matrix and a second 2×2 mother code matrix for 4×4 transmit-receive antenna structure, wherein the first 2×2 mother code matrix is associated with a first set of reference sequences and a first set of corresponding transmit power levels and the second 2×2 mother code matrix is associated with a second set of reference sequences and a second set of corresponding transmit power levels.

[0124] In some example embodiments, the first apparatus further comprises: means for performing a precoding operation on the generated reference sequence by using a 4×4 precoding matrix constructed by a 2×2 identity matrix.

[0125] In some example embodiments, the first apparatus further comprises: means for generating the reference sequence based on a first 2×2 mother code matrix, a second 2×2 mother code matrix, a third 2×2 mother code matrix and a fourth 2×2 mother code matrix for 8×8 transmit-receive antenna structure, wherein the first 2×2 mother code matrix is associated with a first set of reference sequences and a first set of corresponding transmit power levels, the second 2×2 mother code matrix is associated with a second set of reference sequences and a second set of corresponding transmit power levels, the third 2×2 mother code matrix is associated with a third set of reference sequences and a third set of corresponding transmit power levels and the fourth 2×2 mother code matrix is associated with a fourth set of reference sequences and a fourth set of corresponding transmit power levels.

[0126] In some example embodiments, the first apparatus further comprises: means for performing a precoding operation on the generated reference sequence by using an 8×8 precoding matrix constructed by a 4×4 identity matrix.

[0127] In some example embodiments, the first, the second, the third or the fourth set of reference sequences is generated from a seed pilot sequence, and wherein the seed pilot sequence comprises at least one of a Chadoff-Zhu sequence, a Gold sequence, or a Kasami sequence.

[0128] In some example embodiments, the information identifying the at least one reference sequence comprises at least one of the following: a seed pilot sequence associated with the plurality of referencesequences, or a power pattern associated with the plurality of reference sequences, a subset of columns and / or rows of the non-orthogonal code matrix.

[0129] In some example embodiments, the first apparatus comprises a transmitter.

[0130] In some example embodiments, a second apparatus capable of performing any of the method 700 (for example, the second apparatus 120 in FIG. 1) may comprise means for performing the respective operations of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 120 in FIG.1.

[0131] In some example embodiments, the second apparatus comprises means for receiving, from a first apparatus, at least one reference sequence that is at least partly non-orthogonal and information identifying the at least one reference sequence; and means for performing an estimation on at least one channel between the first apparatus and the second apparatus at least partially based on a post- coding operation performed on the at least one reference sequence.

[0132] In some example embodiments, the second apparatus further comprises: means for performing the post-coding operation on the at least one reference sequence by using a post-coding matrix which is a transpose matrix of a pre-coding matrix for pre-coding the at least one reference sequence; and means for obtaining an association between the at least one reference sequence and a plurality of reference sequences and corresponding transmit power levels; and means for estimating the at least one channel by using a characteristic of a block-wise orthogonal matrix generated based on at least one post-coded reference sequence and the association.

[0133] In some example embodiments, the 4×4 precoding matrix is constructed by a 2×2 identity matrix for 4×4 transmit-receive antenna structure.

[0134] In some example embodiments, the 8×8 precoding matrix is constructed by a 4×4 identity matrix for 8×8 transmit-receive antenna structure.

[0135] In some example embodiments, the information identifying the at least one reference sequence comprises at least one of the following: a seed pilot sequence associated with the plurality of reference sequences, or a power pattern associated with the plurality of reference sequences, a subset of columns and / or rows of the non-orthogonal code matrix.

[0136] In some example embodiments, the second apparatus comprises a receiver.

[0137] FIG.8 is a simplified block diagram of a device 800 that is suitable for implementing example embodiments of the present disclosure. The device 800 may be provided to implement a communication device, for example, the first apparatus 110 or the second apparatus as shown in FIG. 1. As shown, the device 800 includes one or more processors 810, one or more memories 820 coupled to the processor 810, and one or more communication modules 840 coupled to the processor 810.

[0138] The communication module 840 is for bidirectional communications. The communicationmodule 840 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 840 may include at least one antenna.

[0139] The processor 810 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 800 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.

[0140] The memory 820 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) 824, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random-access memory (RAM) 822 and other volatile memories that will not last in the power-down duration.

[0141] A computer program 830 includes computer executable instructions that are executed by the associated processor 810. The instructions of the program 830 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 830 may be stored in the memory, e.g., the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

[0142] The example embodiments of the present disclosure may be implemented by means of the program 830 so that the device 800 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 7. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0143] In some example embodiments, the program 830 may be tangibly contained in a computer readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer readable medium to the RAM 822 for execution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0144] FIG.10 shows an example of the computer readable medium 1000 which may be in form of CD,DVD or other optical storage disk. The computer readable medium 1000 has the program 830 stored thereon.

[0145] Generally, 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, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although 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, apparatus, 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.

[0146] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules 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.

[0147] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general-purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, 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.

[0148] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0149] 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, apparatus, 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.

[0150] Further, although 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, although 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. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub- combination.

[0151] 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

WHAT IS CLAIMED IS:

1. A first apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: determine a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix; and transmit, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

2. The first apparatus of claim 1, wherein the non-orthogonal code matrix comprises a non- orthogonal ABBA code matrix.

3. The first apparatus of claim 1 or 2, wherein the first apparatus is caused to: generate a reference sequence based on a first 2×2 mother code matrix and a second 2×2 mother code matrix for 4×4 transmit-receive antenna structure, wherein the first 2×2 mother code matrix is associated with a first set of reference sequences and a first set of corresponding transmit power levels and the second 2×2 mother code matrix is associated with a second set of reference sequences and a second set of corresponding transmit power levels.

4. The first apparatus of claim 3, wherein the first apparatus is caused to: perform a precoding operation on the generated reference sequence by using a 4×4 precoding matrix constructed by a 2×2 identity matrix.

5. The first apparatus of claim 1 or 2, wherein the first apparatus is caused to: generate the reference sequence based on a first 2×2 mother code matrix, a second 2×2 mother code matrix, a third 2×2 mother code matrix and a fourth 2×2 mother code matrix for 8×8 transmit- receive antenna structure, wherein the first 2×2 mother code matrix is associated with a first set of reference sequences and a first set of corresponding transmit power levels, the second 2×2 mothercode matrix is associated with a second set of reference sequences and a second set of corresponding transmit power levels, the third 2×2 mother code matrix is associated with a third set of reference sequences and a third set of corresponding transmit power levels and the fourth 2×2 mother code matrix is associated with a fourth set of reference sequences and a fourth set of corresponding transmit power levels.

6. The first apparatus of claim 5, wherein the first apparatus is caused to: perform a precoding operation on the generated reference sequence by using an 8×8 precoding matrix constructed by a 4×4 identity matrix.

7. The first apparatus of any of claims 3-6, wherein the first, the second, the third or the fourth set of reference sequences is generated from a seed pilot sequence, and wherein the seed pilot sequence comprises at least one of a Chadoff-Zhu sequence, a Gold sequence, or a Kasami sequence.

8. The first apparatus of claim 1, wherein the information identifying the at least one reference sequence comprises at least one of the following: a seed pilot sequence associated with the plurality of reference sequences, or a power pattern associated with the plurality of reference sequences, a subset of columns and / or rows of the non-orthogonal code matrix.

9. The first apparatus of any of claims 1-8, wherein the first apparatus comprises a transmitter.

10. A second apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: receive, from a first apparatus, at least one reference sequence determined at least partly based on a parametrization of a non-orthogonal code matrix and information identifying the at least one reference sequence; and perform an estimation on at least one channel between the first apparatus and thesecond apparatus at least partially based on a post-coding operation performed on the at least one reference sequence.

11. The second apparatus of claim 10, wherein the second apparatus is caused to: perform the post-coding operation on the at least one reference sequence by using a post- coding matrix which is a transpose matrix of a pre-coding matrix for pre-coding the at least one reference sequence; and obtain, from the information, an association between the at least one reference sequence and a plurality of reference sequences and corresponding transmit power levels; and estimate the at least one channel by using a characteristic of a block-wise orthogonal matrix generated based on at least one post-coded reference sequence and the association.

12. The second apparatus of claim 11, wherein the 4×4 precoding matrix is constructed by a 2×2 identity matrix for 4×4 transmit-receive antenna structure.

13. The second apparatus of claim 11, wherein the 8×8 precoding matrix is constructed by a 4×4 identity matrix for 8×8 transmit-receive antenna structure.

14. The second apparatus of any of claims 10-13, wherein the information identifying the at least one reference sequence comprises at least one of the following: a seed pilot sequence associated with the plurality of reference sequences, or a power pattern associated with the plurality of reference sequences. a subset of columns and / or rows of the non-orthogonal code matrix.

15. The second apparatus of any of claims 9-14, wherein the second apparatus comprises a receiver.

16. A method comprising: determining, by a first apparatus, a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix; andtransmitting, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

17. A method comprising: receiving, by a second apparatus, at least one reference sequence determined at least partly based on a parametrization of a non-orthogonal code matrix and information identifying the at least one reference sequence; and performing an estimation on at least one channel between the first apparatus and the second apparatus at least partially based on a post-coding operation performed on the at least one reference sequence.

18. A first apparatus comprising: means for determining a plurality of reference sequences at least partly based on a parametrization of a non-orthogonal code matrix; and means for transmitting, to a second apparatus, at least one reference sequence from the plurality of reference sequences and information identifying the at least one reference sequence.

19. A second apparatus comprising: means for receiving at least one reference sequence determined at least partly based on a parametrization of a non-orthogonal code matrix and information identifying the at least one reference sequence; and means for performing an estimation on at least one channel between the first apparatus and the second apparatus at least partially based on a post-coding operation performed on the at least one reference sequence.

20. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of claim 16 or the method of claim 17.

Images