WO2025095823A1

WO2025095823A1 - Adaptive channel estimation

Info

Publication number: WO2025095823A1
Application number: PCT/SE2023/051097
Authority: WO
Inventors: Ke Wang Helmersson; Pål FRENGER; Anders Helmersson
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-11-01
Filing date: 2023-11-01
Publication date: 2025-05-08
Anticipated expiration: 2026-05-01

Abstract

The disclosure relates to a node in a radio network, the node comprising a processor and a memory, the memory containing instructions executable by the processor whereby the node is operative to generate reference symbol sequences (P) for a time interval by obtaining required number of reference symbol sequences (K) for the time interval, obtaining an orthogonality metric (c), obtaining allocated pilot resources (R) and generating reference symbol sequences (P) using the required number of reference sequences (K), the orthogonality metric (c) and the allocated pilot resources (R), allocate the generated reference symbol sequences (P) to a radio access node and a user equipment, UE, initiate transmission of a signal between the radio access node and the UE.

Description

ADAPTIVE CHANNEL ESTIMATION

TECHNICAL FIELD

The present disclosure relates to adaptive channel estimation. In particular, to adaptive generation of reference symbol sequences.

BACKGROUND

In modern radio networks there is a need for increased performance in capacity, coverage, and signal quality. One way to achieve this is the introduction of multiple input, multiple output, (MIMO) technology.

This has led to the introduction of active antenna array systems, AAS, at both access node and user equipment, UE, sides to improve performance. In particular, development now addresses performance of radio channels between radio access nodes and User Equipment, UE.

The introduction of such techniques infers the need for estimation of an increasing number of radio channels. Channel estimation is typically carried out by transmitting signals with known characteristics, referred to as reference symbols or pilot signals. To separate reference symbol sequences transmitted from different antennas, e.g., in an AAS, orthogonal reference symbol sequences are required, where the number of orthogonal reference symbol sequences required is proportional to the number of transmitting antennas used.

However, having a large number of orthogonal reference symbol sequences requires more resources being allocated to enable longer reference symbol sequences. Conventional solutions therefore attempt to re-use a static number of available reference symbol sequences. This has the drawback of pilot contamination.

Thus, there is a need for an improved method for channel estimation.

An object of the disclosure is to address the above-mentioned shortcomings of conventional solutions.

SUMMARY OF THE DISCLOSURE

The above-described drawbacks are overcome by the subject matter described herein. Further advantageous implementation forms of the disclosure are described herein. The disclosure is set out in the appended set of claims.

According to a first aspect of the present disclosure a node in a radio network is provided, the node comprising a processor and a memory, the memory containing instructions executable by the processor whereby the node is operative to: generate reference symbol sequences for a time interval by obtaining required number of reference symbol sequences for the time interval, obtaining an orthogonality metric, obtaining allocated pilot resources and generating reference symbol sequences using the required number of reference sequences, the orthogonality metric and the allocated pilot resources, allocate the generated reference symbol sequences to a radio access node and a user equipment, UE, initiate transmission of a signal between the radio access node and the UE.

In one embodiment of the first aspect, the node is further operable to: generate the reference symbol sequences by combining a first set of binary sequences and a second set of binary sequences, wherein the first set of binary sequences have a first number of members, wherein the members have a length, wherein positions within the binary sequences being allocated a value of one coincide in at most a second number of positions, wherein the second set of binary sequences have a unit norm of the length and an orthogonality metric less or equal than a threshold equal to a fraction defined as the second number of positions divided by the length.

In one embodiment of the first aspect, the first set of binary sequences are generated as difference sets defined by the first number, the length, and second number of positions.

In one embodiment of the first aspect, the difference sets are defined as:

where i is an indicium, k is the length of members of the first set of binary sequences and D is the difference set.

In one embodiment of the first aspect, the difference set is adapted to a target length of reference symbols by deleting columns of the difference sets.

In one embodiment of the first aspect, the difference set is adapted to a target number of members by deleting rows of the difference set, where in the first set of binary sequences are generated as extended difference sets defined by the first number, the length, the second number of positions, and the target number of members.

According to a second aspect, a computer-implemented method is provided and performed by a node in a radio network, the method comprising: generating reference symbol sequences for a time interval by obtaining required number of reference sequences for the time interval, obtaining an orthogonality metric, obtaining allocated pilot resources and generating reference symbol sequences using the required number of reference symbol sequences, the orthogonality metric and the allocated pilot resources, allocating the generated reference symbol sequences to a radio access node and a user equipment, UE, initiating transmission of a signal between the radio access node and the UE.

In one embodiment according to the second aspect, generating reference symbol sequences comprises: combining a first set of binary sequences and a second set of binary sequences, wherein the first set of binary sequences have a first number of members, wherein the members have a length, wherein positions within the binary sequences being allocated a value of one coincide in at most a second number of positions, wherein the second set of binary sequences have a unit norm of the length and an orthogonality metric less or equal than a threshold equal to a fraction defined as the second number of positions divided by the length.

In one embodiment according to the second aspect, the first set of binary sequences are generated as difference sets defined by the first number, the length, and second number of positions.

In one embodiment according to the second aspect, the difference sets are defined as:

In one embodiment according to the second aspect, the difference set is adapted to a target length of reference symbols by deleting columns of the difference sets.

In one embodiment according to the second aspect, the difference set is adapted to a target number of members by deleting rows of the difference set, where in the first set of binary sequences are generated as extended difference sets defined by the first number, the length, the second number of positions, and the target number of members.

According to a third aspect, a method is provided and performed by a user equipment UE, the method comprising: receiving a control signal indicative of generated reference symbol sequences, transmitting to a radio access node, or receiving from a radio access node using the received reference symbol sequences. In one embodiment according to the third aspect, the method further comprises providing user data; and forwarding the user data to a host via the transmission to the network node.

According to a fourth aspect, a user equipment, UE, in a radio network is provided, the user device comprising: a processor, and a memory, said memory containing instructions executable by said processor, whereby said user device is operative to perform the method according to the third aspect.

According to a fifth aspect, a host is provided and is configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps: receive a control signal indicative of generated reference symbol sequences (P), transmit to a radio access node or receiving from a radio access node using the received reference symbol sequences (P), to receive the user data from the host.

In one embodiment according to the fifth aspect, the cellular network further includes a network node configured to communicate with the UE to transmit the user data to the UE from the host.

In one embodiment according to the fifth aspect, the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

According to a sixth aspect, a method is provided and implemented by a host operating in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the UE performs any of the steps: receiving a control signal indicative of generated reference symbol sequences, transmitting to a radio access node or receiving from a radio access node using the received reference symbol sequences, to receive the user data from the host. In one embodiment according to the sixth aspect, the method further comprises: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

In one embodiment according to the sixth aspect, the method further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

In one embodiment according to the sixth aspect, the method further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application.

According to a seventh aspect, a host is provided and configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a network node in a cellular network for transmission to a user equipment (UE), the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to: generate reference symbol sequences for a time interval by obtaining required number of reference sequences for the time interval, obtaining an orthogonality metric, obtaining allocated pilot resources and generating reference symbol sequences using the required number of reference symbol sequences, the orthogonality metric and the allocated pilot resources, allocate the generated reference symbol sequences to a radio access node and a user equipment, UE, initiate transmission of a signal between the radio access node and the UE, to transmit the user data from the host to the UE.

In one embodiment according to the seventh aspect, the processing circuitry of the host is configured to execute a host application that provides the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application to receive the transmission of user data from the host.

According to a eighth aspect, a host is provided and configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the network node isa operable to: process circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a network node in a cellular network for transmission to a user equipment (UE), the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to: generating reference symbol sequences for a time interval by obtaining required number of reference sequences for the time interval, obtaining an orthogonality metric, obtain allocated pilot resources and generating reference symbol sequences using the required number of reference symbol sequences, the orthogonality metric and the allocated pilot resources, allocating the generated reference symbol sequences to a radio access node and a user equipment, UE, initiating transmission of a signal between the radio access node and the UE, to transmit the user data from the host to the UE.

In one embodiment according to the eighth aspect, the method further comprising, at the network node, transmitting the user data provided by the host for the UE.

In one embodiment according to the eighth aspect, the user data is provided at the host by executing a host application that interacts with a client application executing on the UE, the client application being associated with the host application.

The scope of the disclosure is defined by the claims, which are incorporated into this section by reference. Reference will be made to the appended sheets of drawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.

Fig. 1 illustrates a UE transmitting reference symbol sequences to access points.

Fig. 2 illustrates Time-Division Duplex operation according to one or more embodiments of the present disclosure.

Fig. 3 illustrates reference symbol sequences defined by a table according to one or more embodiments of the present disclosure.

Fig. 4 shows an example of a radio network according to one or more embodiments of the preset disclosure.

Fig. 5 illustrates an example of generating reference symbol sequences P for a time interval according to one or more embodiments of the preset disclosure.

Fig 6A illustrates sequences of a difference set according to one or more embodiments of the preset disclosure.

Fig 6B illustrates indices of non-zero values of elements of a difference set according to one or more embodiments of the preset disclosure. Fig. 7A shows a generic matrix for difference sets.

Fig. 7B illustrates one example how to generate extended difference set for recursively.

Fig. 8A-D Illustrates adaption of reference symbol sequences.

Fig. 9 shows a flowchart of a method according to one or more embodiments of the present disclosure.

Fig. 10 shows a flowchart of a method according to one or more embodiments of the present disclosure.

Fig. 11 shows details of a radio network node according to one or more embodiments of the present disclosure.

Fig. 12 illustrate functional modules of a network node according to the present disclosure.

Fig. 13 shows functional modules of a UE according to one or more embodiments of the present disclosure.

A more complete understanding of embodiments of the disclosure will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments.

DETAILED DESCRIPTION

The present disclosure relates to methods and devices for improving channel estimation.

In brief, the present disclosure adapts the number of reference symbol sequences by considering the required number of reference symbols, an orthogonality metric, and allocated resources for a time interval, by varying the degree of orthogonality between the reference symbols.

In the context of this disclosure the terms reference signal, reference symbol sequence, reference symbol, pilot, pilot sequence, and pilot signal will be used interchangeably. The terms typically signify a symbol and/or signal and/or sequence with known characteristics. This enables a receiving node to compare characteristics of a received signal to ideal and predetermined characteristics of the signal at the time of transmittal. Thereby, a channel estimate can be derived.

The area of the disclosure is laid out below:

Channel estimation is foundational to perform coherent transmission in the downlink and coherent reception in the uplink in multiple input, multiple output , MIMNO, networks, e.g., distributed M IM O/D- Ml MO or multiuser MIMO/MU-MIMO networks. Since radio channels in the network typically change from one coherence block to another, channel estimation of the channels typically needs to be performed for all active users in every coherence block. A coherence block is defined as a number of subcarriers and a time interval over which the channel response can be approximated as constant and flat fading.

Channel estimation may be carried out, e.g., based on uplink, UL, reference symbol sequences. See Fig. 1.

Fig. 1 shows how a redefined reference symbol sequence Sk is transmitted UL from a UE antenna, and any other receiver antennas in the network can simultaneously receive the transmission and compare it with a predefined reference symbol sequence, e.g., received by antennas at the access points APi, APi, APL. The channel Hik, hik, hi_k between the transmitting antenna and receiving antennas can then be estimated using the known characteristics of the predefined reference symbol sequence Sk. To separate the reference symbol sequences received from two transmitting antennas, then two orthogonal or nearly orthogonal reference symbol sequences are required. The number of orthogonal reference symbol sequences required is thus normally proportional to the number of transmitting antennas, .e.g., active in a coherence block.

Fig. 2 illustrates Time-Division Duplex (TDD) operation according to one or more embodiments of the present disclosure.

In the case of TDD operation, as shown in Fig. 2, the uplink and downlink channels are assumed to be reciprocal. In otherwords, an estimated UL channel can represent an estimated channel for a corresponding DL channel. Each user equipment, UE sends a sequence of reference symbol sequences, and each access point (AP) APi, APi, APL receives the reference symbol sequences and estimates the channel between antennas of the UEs and antennas of the respective AP, e.g., in each coherence block.

For illustration purposes, only one antenna is depicted per UE in Fig. 1. It is understood that for multiple antenna UEs, multiple reference symbol sequences are required to estimate the channels between the transmit antennas and receiver antennas. As shown in Fig. 2 the reference symbol sequences will consume some of the radio resources in each coherence block. Let t_P be the length of the reference symbol sequence resource.

Ideally, each antenna of each UE needs to be assigned a reference symbol sequence that is orthogonal to other reference symbol sequence that are simultaneously assigned, so that no interference is observed in the received reference symbol sequences. However, since the reference symbol sequences consume radio resources, there is a tradeoff between having longer reference symbol sequences, and thereby supporting a large number of UEs ( ) and assuring that reference symbol sequences are orthogonal (or at least have low cross correlation).

A common conventional solution is to reuse the reference symbol sequences if a total number of antennas at the transmission side is larger than T_P . For example, assuming one antenna at UE side, there are K active UEs that are scheduled for transmission. If K >T_P it is necessary to reuse the reference symbol sequences. I.e., to allow more than one UE to share the same reference symbol sequence.

The reuse of reference symbol sequences causes non-orthogonality of reference symbol sequences and the interference generated by antennas sharing reference symbol sequence is known as pilot contamination in the literature. The pilot contamination reduces not only the quality of channel estimation but also makes the channel estimates correlated for antennas sharing reference symbol sequence.

In the present disclosure, a method is presented to design reference symbol sequences with configurable non-orthogonality and configurable resource usage to be used for channel state information acquisition in a multi-user MIMO system. The amount of non-orthogonality is adapted based on:

-The number of reference symbol sequences required in a time interval, e.g., a number of coscheduled MU -Ml MO UEs requiring CSI acquisition in a time interval.

-The amount of pilot resources available in said time interval. I.e., the total amount of physical resources allocated to reference symbol sequences for CSI acquisition.

-The available number of almost orthogonal reference symbol sequences can be extended when more reference symbol sequences are needed without extending the number of resources allocated to reference symbol sequences.

The pilot/ reference symbol sequences orthogonality can be defined mathematically, allowing design of a set of reference symbol sequences that are “as orthogonal as possible” given the allocated pilot/reference symbol sequences resources.

Furthermore, the number of almost orthogonal reference symbol sequences can be dynamically adjusted or adapted based on the number of active antennas of users who are scheduled for transmission or reception in a coherence block.

The resources allocated to reference symbol sequences can be adjusted or adapted based on the correlation of the current set of reference symbol sequences/reference symbol sequences.

-High correlation (high contamination) -> increase the reference symbol sequences resources. -Low correlation (high cost of pilot resource) -> decrease the reference symbol sequences resources.

We also disclose a method for signaling reference symbol sequences resources, in accordance with the present disclosure, to the UE.

In embodiments, a reference symbol sequence is signaled to the UE by providing parameters needed for generating or identifying the reference symbol sequences. The needed parameters may be signaled on a downlink control channel, e.g., physical downlink control channel, PDCCH. Since the code construction is predetermined and can be expressed as a function of a small number (at least one) of parameters, any reference symbol sequence can be defined by first identifying a set of sequences, e.g., a set of sequences defined by a table, from which the reference symbol sequence is to be selected from, and then identifying the reference symbol sequence within the set using an index/indicium.

Advantages of the present disclosure include at least:

The number of almost orthogonal reference symbol sequences can be dynamically adjusted/adapted based on reference symbol requirements. E.g., the number of antennas of active users who are scheduled for transmission or reception, e.g., scheduled in a coherence block.

The overhead of reference symbol sequences can be dynamically adapted based on needs. I.e., reduced when a current number of reference symbol sequences are not needed or increased when a current number of reference symbol sequences are not sufficient.

The number of available reference symbol sequences can be increased in a controlled way when more reference symbol sequences are needed.

Equally distributed and intentionally controlled non-orthogonality is achieved between the reference symbol sequences used by different UEs for channel state information acquisition in a MIMO system.

The disclosure is especially useful to enable resource efficient support for multi-antenna UEs where the maximum number of required reference symbol sequences can be very large. The number of reference symbol sequences required is at least the number of UEs times number of antenna elements per UE.

A more detailed description of the disclosure follows below.

As mentioned previously, channel estimation is foundational to perform coherent transmission in the downlink and coherent reception in the uplink in a D-MIMO and MU -Ml MO network. The radio channels change from time to time since the transmitter, receiver, and objects in the wireless propagation environment typically moves. However, if we consider a sufficiently short time interval, the channel can be approximated as constant and therefor the wireless communication can be assumed to be time-invariant during this short time interval. This time interval is referred to as channel coherence time. The channel coherence time can be determined by the speed of movement of a UE and is typically a few milliseconds for UEs in mobile networks.

To be able to use channel properties for calculating precoding and combining weights, it is necessary to estimate the channel once per coherence time internal for each transmitting antenna. Within coherence time interval, the channel can be described by a finite impulse response (FIR) filter where each term of the impulse response describes one distinguishable propagation path in a multipath environment with a distinct time delay and pathloss. Considering a sufficiently narrow frequency range, e.g., a small number of resource blocks, the channel can be considered constant. Hence the channel coherence bandwidth can be defined as the frequency interval in which the frequency response is approximately constant. Thus, a coherence block is defined as frequency range (a number of subcarriers) and a time interval (a number of symbols) over which the channel response can be approximated as constant and flat fading. In other words, a coherence block is defined by coherence time and coherence bandwidth.

Channel estimation

The channels between a UE and an AP typically need to be estimated for each coherence block. In a MIMO network, the channel estimation is carried out based on reference symbol sequences, see Fell Hittar inte referenskalla.. A cooperative MIMO, C-MIMO, a distributed MIMO, D-MIMO or a multi-user MIMO, MU-MIMO, network may be considered.

In each coherence block there are a number K user equipment, UE, who are scheduled for transmission in the downlink or for reception in the uplink, and N antenna elements in the system to be used for these K UE. To simplify the description, we assume each UE has one antenna, but this doesn’t limit the present disclosure. When there are multiple antennas at UE side, we can simply multiply the number of antennas of UE with number of UE as M x K, M > 1.

The channel, H_nk e (C^/Vx/f, is the channel between UE_k, k e [1, R] and receiving antenna n e [1, N], The channel H_nk is often assumed to have a normal distribution H_nk = N(0_NXK, R) where R = diag[R₁₍ R_K], and R_k = R_k E C^NxN . In TDD systems, the uplink and downlink channels are assumed to be identical (reciprocity assumption) except for an uncertainty in phase.

Each UE sends a sequence of reference symbol sequences,

over T_P symbols, which is also called the length of reference symbol sequences. The reference symbol sequences should, if possible, be orthogonal, that is

= 0 when i A k. If the number of users, K, K < T_P reference symbol sequences can be, for instance, Hadamard coded. If K exceeds t_P it is not possible to find unique orthogonal reference symbol sequences for each user.

One common way to handle this situation is to allocate the same reference symbol sequence to some users. This scheme is called pilot reuse. Pilot reuse gives very poor performance for users with the same reference symbol sequences allocated and results in pilot contamination.

We propose in this disclosure to use a bigger set of reference symbol sequences that are almost orthogonal, such that

^TP^C assuming normalized reference symbol sequences

(01^{2 = T}P ^anc* ^a parameter c > 0, which is defined and described in more details below. We can find more reference symbol sequences to users by selecting T_P and c. For instance, for any t_P, we can find t_P + 1 reference symbol sequences that achieve c = 1/T_P. Another example is for t_P = 16, for which we can find 144 reference symbol sequences with c = 1/4.

For arbitrary reference symbol sequences, the channel may be estimated e.g., by a Kalman filter. A Kalman filter uses measurements, y(t) = C(t)x(t) + e(t), to estimate the state, x(t). In our case, the received signals from N antennas, y(t) =

+ e(t), are used for estimating the channel. Consider the state vector x(t) G <C^NK JS a complex vector containing all elements of unknown channel H G

which is a block-diagonal matrix containing N repeated sub-blocks of (/> t)P^², where (t) is the known reference symbol sequences and P_o is an initial value of the covariance matrix.

Reference symbol sequence generation

Based on Time-Division Duplex (TDD) operation as shown in Fell Hittar inte referenskalla., and assuming uplink and downlink channels to be identical except for an uncertainty in phase (reciprocity assumption), then each antenna of each UE sends a reference symbol sequence and each AP use the received reference symbol sequences to estimate the channel between antennas of UE and AP, e.g., in each coherence block or during a time interval. Ideally, the reference symbol sequences should be orthogonal. This requires that every UE antenna needs to be assigned a reference symbol sequence that is orthogonal to the reference symbol sequences assigned to other antennas of UEs, such that no interference occurs in received reference symbol sequences. However, the reference symbol sequences occupy uplink resources, which must be considered as limited. If the length of the reference symbol sequences is limited to T_P, a maximum of T_P antennas of the UEs can be served at the same time. In a practical D-MIMO or MU -Ml MO network the number of active UEs, say K users, can be sometimes K > T_P and sometimes K < r_P. For simplicity, we assume one antenna at UE side in this example.

The disclosure herein proposes to generate almost orthogonal reference symbol sequences based the performance requirement and resource availability. The reference symbol sequences should be as orthogonal as possible at the cost of uplink resources. To define what is almost or near orthogonality a parameter c is introduced, which herein is referred to as pilot correlation factor or orthogonality metric.

To formulate a general term of reference symbol sequence generation mathematically, the length of a reference symbol sequence is denoted by n, which is the same as T_P that is commonly used in literature. The reference symbol sequence is denoted by <p, and can be formulated mathematically as a vector that contains n elements.

The correlation factor between two reference symbol sequences can then be formulated as the angle between two vectors, c = | cos(A< >) |, If two vectors are orthogonal, the angle or the difference between two vectors, is A = TT/2, then there is no correlation between these two reference symbol sequences, and hence the correlation factor c = 0.

It is not always possible to achieve perfect orthogonality between reference symbol sequences assigned to different UEs. Instead, we should accept some correlation between the reference symbol sequences. If some small correlation factor c is accepted, then more reference symbol sequences can be generated.

Herein these sequences are referred to as reference symbol sequences/reference symbol sequences or nearly orthogonal reference symbol sequences. The available number of nearly orthogonal reference symbol sequences varies depending on the correlation factor. The higher correlation factor c, the more reference symbol sequences can be found. Mathematically this can be formulated as a scalar product of any two vectors which are guaranteed to be less than or equal to the correlation factor such as l d < c(/)_k*(/)_k, i * k. For example, if c = 0 we can find n vectors that are orthogonal, hence n orthogonal reference symbol sequences can be generated. if we increase the correlation factor such that: c = 1/n, we can find n + 1 vectors (which is called simplex set) that achieve a scalar product of — 1/n for normalized vectors, hence we can generate n + 1 reference symbol sequences with correlation factor 1/n.

For a higher value of c, more vectors can be found within the set using the method disclosed herein. Hence, the larger the values of c the more reference symbol sequences are available for supporting channel state acquisition related to more UEs.

The disclosed method is formulated as following:

A set of nearly orthogonal reference symbol sequences can be generated by combining: a first set of reference symbol sequences of length n each with k non-zero elements, where any two of said reference symbol sequences coincide in at most positions (e.g., = 1, 2,

and a second set of reference symbol sequences of complex values with unit norm, of length k, with a cross correlation less than or equal to a threshold, c = /k.

To further describe how to construct the reference symbol sequences using the disclosed method, some definitions for terms used in the subsections below are given. Further examples are also provided to show how to generate reference symbol sequences based on the disclosed method.

Fig. 4 shows an example of a radio network 100 according to one or more embodiments of the preset disclosure. The radio network 100 may e.g., be an access point, AP. The radio network 100 comprises at least a network node 120 configured to receive/transmit radio signals from/to user devices, UE, 110 in the radio network 100. The at least one network node 102 comprises one or more antennas A1-A4 and circuitry capable of performing radio reception/transmission.

The user devices are typically user operated devices, such as user equipment, UE, 110. The UE comprises one or more antennas A5-A8 and circuitry capable of performing radio reception/transmission.

As can be seen in Fig. 4, reference symbol sequences P1-P4 are transmitted from the UE 110 to the AP 120, and optionally reference symbol sequences P5-P8 are transmitted from the AP 120 to the UE 110. The received reference symbol sequences can then be used for channel estimation purposes. Fig. 5 illustrates an example of generating reference symbol sequences P for a time interval according to one or more embodiments of the preset disclosure. The time interval may e.g., be coherence time of a coherence block.

A node 500 in the radio network 100 obtains a required number of reference symbol sequences K for the time interval. The time interval may e.g., be a time interval equal to a coherence time of a coherence block. In one example, the required number of reference symbol sequences K indicate how many reference symbol sequences that are needed, e.g., needed for the scheduled UEs during a coherence time of a coherence block. It is understood that any suitable time interval could be used, other than the coherence time.

The node 500 then obtains an orthogonality metric (c). It can be seen as the orthogonality metric (c) is indicative of an acceptable degree of orthogonality between reference symbol sequences.

The node 500 then obtains allocated pilot resources (R) for the TTI. The resources may e.g., be indicative of an allocated length of the reference symbol sequences.

The node 500 then generate reference symbol sequences P for the time interval using the required number of reference symbol sequences K, the orthogonality metric c and the allocated pilot resources R. The generate reference symbol sequences /’are illustrated in Fig.

5 as a matrix with dimensions MxNof sequences Pll-PMN.

Generating the first set of reference symbol sequences

The disclosed method comprises to combine two sets of sequences in order to generate nearly orthogonal reference symbol sequences in a flexible and controlled manner. In this sub-section methods on how to generate the first set of sequences are described.

Difference sets

The first set of sequences can be defined by differences sets, further described in “Difference sets - Dan Gordon” (dmgordon.org) https://www.dmgordon.org/diffset/. The difference set is a term used in combinatorics, which is an area of mathematics. It is defined by n subsets of size k from a larger group of size n, there are n elements in the larger group. Any two subsets have exactly elements in common and any two elements are simultaneously contained in exactly subsets. The difference sets are characterized by a triple (n, fc, ). The differences between two elements, d_L — dj, in the set generates all non-zero elements in the group of n elements exactly times. Some examples are given below on how to generate the difference sets in the present disclosure. As a first example, assume that it is desirable to generate a set of reference symbol sequences of length n = 7, and allow the correlation factor to be c = 1/3. The present disclosure then applies the difference set triple (h,k,X) = (7,3,1) using A = 1 to generate reference symbol sequences with correlation factor c = 1/3 in the following way:

A first sequence of three non-zero elements, k = 3, is distributed over seven positions, at position 1, 2, and in a first element/row. The sequence is then repeated on the following rows by cyclic permutations of the previous row. In this way, seven such sequences can be generated with three non-zero elements. An essential property is that any two sequences from this set has only one position in common. For instance, row 1 (where elements 1,2,4 are 1) and row 3 (where elements 3,4,6 are 1) have only one position 4 in common as A = 1.

Fig 6B illustrates indices of non-zero members/values of elements of a difference set according to one or more embodiments of the preset disclosure. In other words, the sequences illustrated in Fig. 6A can be expressed in a more compact manner by listing indices of nonzero members of elements/rows. In Fig.6B it can be seen that row 1 [12 4] and row 3 [346] have the index 4 in common. I.e., only one non-zero members position (4) in common.

As a second example, assume a set of reference symbol sequences of length n = 21 needs to be generated with correlation factor c = 1/5:

Now the difference set triple is (n, k,A) = (21,5,1), a sequence of five non-zero elements in 21 positions are 1, 2, 5, 15, 17 together with 21 cyclic permutations.

411001000000000101000 oh

[01100100000000010100 0]

05(21,5,1) = < [001100100000000010100] ► . [10010000000001010000 1]

Or equivalently using more compact indices of non-zeros as

Note that using cyclic permutations of one starting sequence is one way to generate a difference set and that this method works only in special cases. There are other methods can be used to generate difference set. A generic method is proposed below when the extended difference sets are introduced.

Extended Difference sets

In this part of the disclosure, the difference set described above is generalized to be more relaxed in terms of the actual number of the reference symbol sequences to be generated. This is from here on referred to as an extended difference set. An extended difference set is defined by selecting m subsets of k non-zero elements from a length of n group such that any two subsets have at most A elements in common. An extended difference set is characterized by (n,m,k,A).

For instance, for a length of n = 4 group {1, 2, 3, 4}, the extended difference set with A = 1 and k = 2 consists of m = 6 subsets: {{1,2}, {1,3}, {1,4}, {2,3}, {2,4}, {3,4}]. Hence this extended difference set is characterized by (4,6, 2,1).

The extended difference set relaxes the number of subsets to m instead of the length of the group n. The difference set is thus a special case of extended difference set when m = n. This relaxation also provides a flexibility to generate different length of reference symbol sequences. To illustrate this, we further propose a generic solution to generate extended difference sets. Using this solution, the extended difference set can be constructed reclusively by a generic matrix of size k + 1 x k

Fig. 7A shows a generic matrix for difference sets.

I the example shown in Fig 7B, k = 5 and the generic matrix (Fell Hittar inte referenskalla.) is used recursively by iterating from the starting matrix D .

From the generic matrix D in (7) we can see that that the maximum length of codes is n_max = 15, which is calculated from

+ l)/2. The advantage of using the generic matrix is that we can also generate other lengths of reference symbol sequences by truncating the generic matrix. For example, by truncating the last two rows in D_s we obtain an extended difference set (n, m, 5,1) = (14,4,5,1)

A matrix with two truncated rows is shown in Fig. 8A.

The length of reference symbol sequences can be further reduced by truncating more rows in D₅ to obtain extended difference sets.

A matrix with three truncated rows is shown in Fig. 8B.

A matrix with four truncated rows is shown in Fig. 8C.

A matrix with five truncated rows is shown in Fig. 8D.

Different lengths of reference symbol sequences using the generic matrix (Fell Hittar inte referenskalla.)-(7) are given by the last column or the last row of the generic matrix.

The generic matrix (Fell Hittar inte referenskalla.) for any given parameter k can also be written as a look-up table, which is shown in Fig. 3.

The look-up table has the advantage that it is easier to implement in the devices when the network side, e.g., a node as the scheduler, needs to inform the UE which extended difference set each UE should use to generate nearly orthogonal reference symbol sequence for the channel estimation.

In the table the length of the reference symbol sequences is given in the last column n. The length of pilots can be varied from k up to n_max = + l)/2. By truncating the generic matrix, more extended difference sets can be produced for different number of m, from m = 1 to k, which is given in the first column, they can be used for generating shorter length of reference symbol sequences, n_max — 1, ■■■ , k. For general case, (n, m, k, 1) = ( — - — , k +

1, k, 1) can be truncated to produce difference sets for (n — 1, k — 1, k, 1), (n — 2, k —

2, k, 1),..., (3k — 3,3, k, 1), (2k — 1,2, k, 1) and (k, 1, k, 1).

Generating the second set of sequences

In embodiments of the disclosed method, two sets of sequences are combined in order to generate nearly orthogonal reference symbol sequences in a flexible and controlled manner. In this sub-section we describe methods on how to generate the second set of sequences.

Nearly Orthogonal codes

In the proposed method, the second set of sequences is to generate codes with unit norm. One solution is to use the discrete Fourier transform (DFT) matrix. The DFT transforms a sequence of n numbers into another sequence of complex numbers which provides an n x n mutually orthogonal matrix. The elements of the matrix have unit norm and are given by:

The DFT matrix has the orthogonality property:

H_nH_n = nl_n for any positive integer n where I_n is an n x n identity matrix. Truncate the DFT matrix by removing one column, we obtain a submatrix ff_nX(n-i), each ^row °f ^nx(n-i) ^can be used as the second set of sequences of the submatrix. We call them the DFT codes. These DFT codes can be used as almost or nearly orthogonal reference symbol sequences.

A Hadamard matrix, see “Hadamard Matrix”: https://en.wikipedia.org/wiki/Hadamard_matrix, is a special form of DFT matrix whose entries are either +1 or -1 and whose rows are mutually orthogonal, as well as columns followed by the property of Hadamard matrix:

H_nH^ = nl_n, where n is the size of the matrix and I_n is the n x n identity matrix. The size of a Hadamard matrix must be 1 , 2, or multiples of 4. For instance

and in general H₂i-i H₂i-i

H_2i = for 2 < i E N. (8)

,H₂i-i —H₂i-i

Like the DFT matrix, truncate the Hadamard matrix H_n, n = 2^l, by removing one column we obtained the Hadamard codes from the row vectors of ff_nX(n-i)- We call them the Hadamard codes. The Hadamard codes can be used as the nearly orthogonal reference symbol sequences.

Combining the first set and the second set of sequence

As discussed above, the second set of sequences can be used as nearly orthogonal reference symbol sequences. However, the number of available reference symbol sequences is fixed to the length of the sequence e.g., the number of rows of DFT matrix.

The proposed method provides a flexible trade-off between the length of the reference symbol sequences and orthogonality of the reference symbol sequences. For the given length of the reference symbol sequences, the available number of reference symbol sequences can be increased by combining the first set and second set sequences.

On one hand, the disclosed method enables to generate nearly orthogonal reference symbol sequences when the orthogonal reference symbol sequences are not enough, in the case e.g., there are more UEs, or each UE has more antennas that require more reference symbol sequences. On the other hand, the disclosed method also enables to provide the required number of reference symbol sequences by reducing the length of the reference symbol sequences, hence reduce overhand on the resource.

In most of cases, we can use the difference set (n, k, 1), i.e., A = 1, together with a Hadamard matrix H_k+1. The parameters of difference set provide the length of reference symbol sequences to be n, and number of non-zero elements in the reference symbol sequences to be k. If we apply the generic matrix (Fell Hittar inte referenskalla.) or the table in Fig. 3 to obtain the difference set, the positions of non-zero elements in reference symbol sequences are given by the difference sets such as shown in (Fell Hittar inte referenskalla.)-(7).

The Hadamard codes are obtained by truncating one column in Hadamard matrix H_k+1 and then using the remaining k columns H_k+lxk. The k non-zero elements are then replaced by Hadamard codes H_k+lxk to produce the reference symbol sequences. I.e. the n-th non-zero element in the difference set is replaced with the n-th element in the Hadamard sequence. This combination produces n(k + 1) reference symbol sequences with correlation c = 1/k. In the case when an extended difference set (n, m, k, 1) is used to combine with Hadamard codes, the combination produces m(k + 1) reference symbol sequence with correlation c = 1/k.

The Hadamard codes can be replaced by DFT codes to combine with extended difference set in the similar way.

There is no limitation to use other codes, for instance, the binary codes, see [3] “Binary code:” https://en.wikipedia.org/wiki/Binary_code, to generate nearly orthogonal reference symbol sequences using disclosed method.

Fig. 9 shows a flowchart of a method 900 according to one or more embodiments of the present disclosure. The method 900 may be a computer-implemented method performed by a node in a radio network 100, e.g., a scheduler or an AP. The method comprising:

Step 910: generating reference symbol sequences (P) for a time interval by: obtaining required number of reference symbol sequences K for the time interval, obtaining an orthogonality metric (c), obtaining allocated pilot resources (P), and generating reference symbol sequences (P) using the required number of reference symbol sequences (K), the orthogonality metric (c) and the allocated pilot resources (P).

Step 920: allocating the generated reference symbol sequences (P) to a radio access node and a user equipment, UE,

Step 930: initiating transmission of a signal between the radio access node and the UE.

In one non-limiting example, the time interval comprises coherence time of a coherence block.

The required number of reference sequences K may e.g., be a number of UEs active or scheduled for transmission during the time interval, optionally multiplied by the number of transmit antennas used by the UEs.

The correlation factor , c between two reference symbol sequences may in one example be formulated as the angle between two vectors, c = | cos(A< >) |. In other words, the angle between two reference symbol sequences defined as vectors. If two reference symbol sequences are orthogonal, the angle or the difference between two reference symbol sequences, is A = TT/2, then there is no correlation between these two reference symbol sequences, and hence the correlation factor c = 0. In one non-limiting example, the allocated pilot resources R may be defined as the allocated length of reference symbol sequences.

Additionally, or alternatively, generating the reference symbol sequences P comprises combining a first set of binary sequences and a second set of binary sequences.

Additionally, or alternatively, the first set of binary sequences have a first number n members, wherein the members have a length k, wherein positions within the binary sequences being allocated a value of one coincide in at most a second number A of positions.

Additionally, or alternatively, the second set of binary sequences have a unit norm of the length k and the orthogonality metric c less or equal than a threshold equal to a fraction defined as the second number of A positions divided by the length k.

Additionally, or alternatively, the first set of binary sequences are generated as difference sets defined by the first number (n), the length (/c), and second number (A) of positions. Difference sets are further described in relation to Figures 6A-8D.

Additionally, or alternatively, the difference sets are defined as:

Additionally, or alternatively, the difference set is adapted to a target length of reference symbol sequences by deleting columns of the difference sets. In other words, the length of reference symbol sequences may be adapted to resources allocated to reference symbol sequences.

Additionally, or alternatively, the difference set is adapted to a target number of members (m) by deleting rows of the difference set, where in the first set of binary sequences are generated as extended difference sets defined by the first number (n), the length (Zc) , the second number (A) of positions, and the target number of members (m).

Fig. 10 shows a flowchart of a method 1000 according to one or more embodiments of the present disclosure. The method 1000 is performed by a UE. The method comprises.

Step 1010: receiving a control signal indicative of generated reference symbol sequences (P).

Additionally, or alternatively, the control signal is indicative of parameters needed for generating or identifying the reference symbol sequences. In one example, the parameters are indicative of the required number of reference symbol sequences K, the orthogonality metric c and the allocated pilot resources R. The UE can then generate the reference symbol sequences P using the provided parameters.

In one example, the parameters are indicative of a table identity and an index/indicium, that allows the UE to identify a table and access the reference symbol sequences P using the indicium. Tables are further described in relation to Fig. 3.

Additionally, or alternatively, the control signal comprises a physical downlink control channel, PDCCH.

Step 1020: transmitting to a radio access node 120 or receiving from a radio access 120 node using the received reference symbol sequences P.

In one example, a unique reference symbol sequence is transmitted from each antenna of the UE.

Fig. 11 shows details of a radio network node 1100 according to one or more embodiments of the present disclosure.

The network node 1100 may be in the form of a selection of any of a gNB, a virtual node in a cloud, a network node, a desktop computer, server, laptop, mobile device, a smartphone, a tablet computer, a smartwatch etc. The network node 1100 may comprise processing circuitry 1112. The network node 1100 may optionally comprise or be communicatively coupled to a communications interface 1104 for wired and/or wireless communication. Further, the network node 1100 may further comprise at least one optional antenna (not shown in figure). The antenna may be coupled to a transceiver of the communications interface 1104 and is configured to transmit and/or emit and/or receive wireless signals, e.g., in a wireless communication system.

In one example, the processing circuitry 1112 may be any of a selection of processor and/or a central processing unit and/or processor modules and/or multiple processors configured to cooperate with each-other. Further, the network node 1100 may further comprise a memory 1115. The memory 1115 may contain instructions executable by the processing circuitry 1112, that when executed causes the processing circuitry 1112 to perform any of the methods and/or method steps described herein.

The communications interface 1104, e.g., the wireless transceiver and/or a wired/wireless communications network adapter is configured to send and/or receive data values or parameters as a signal. In an embodiment, the communications interface 1104 communicates directly between nodes or via a communications network. In one or more embodiments the network node ,1100 may further comprise an input device or interface 1117, configured to receive input or indications from a user and output/send a userinput signal indicative of the user input or indications to the processing circuitry 1112. In other words, the input device/interface 1117 receives input or indications from the user and translates this into data that the processing circuitry 1112 can interpret.

In one or more embodiments the network node 1100 may further comprise a display 1118 configured to receive a display signal indicative of rendered objects, such as text or graphical user input objects, from the processing circuitry 1112 and to display the received signal as objects, such as text or graphical user input objects. In other words, the display receives data that the processing circuitry 1112 can interpret and display the data in a format that the user can understand.

In one embodiment the display 1118 is integrated with the user input device/interface 1117 and is configured to receive a display signal indicative of rendered objects, such as text or graphical user input objects, from the processing circuitry 1112 and to display the received signal as objects, such as text or graphical user input objects, and/or configured to receive input or indications from a user and send a user-input signal indicative of the user input or indications to the processing circuitry 1112.

In one or more embodiments the network node 1100 may further comprise one or more additional sensors (not shown).

In embodiments, the processing circuitry 1112 is communicatively coupled to the memory 1115 and/or the communications interface 1104 and/or the input device 1117 and/or the display 1118.

In embodiments, the communications interface and/or transceiver 1104 communicates using wired and/or wireless communication techniques.

In embodiments, the one or more memory 1115 may comprise a selection of a hard RAM, disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a CD or DVD drive (R or RW), or other removable or fixed media drive.

In a further embodiment, the network node 1100 may further comprise and/or be coupled to one or more additional sensors (not shown) configured to receive and/or obtain and/or measure physical properties pertaining to the network node or the environment of the network node and send one or more sensor signals indicative of the physical properties to the processing circuitry 1112.

It is to be understood that a network node comprises any suitable combination of hardware and/or software needed to perform the tasks, features, functions, and methods disclosed herein. Moreover, while the components of the network node are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, a network node may comprise multiple different physical components that make up a single illustrated component (e.g., memory 1115 may comprise multiple separate hard drives as well as multiple RAM modules).

Similarly, the network node 1100 may be composed of multiple physically separate components, which may each have their own respective components.

The communications interface 1104 may also include multiple sets of various illustrated components for different wireless technologies, such as, for example, Global System for Mobile Communications GSM, Wideband Code-Division Multiple Access, WCDMA, Long- Term Evolution, LTE, New Radio, NR, Wireless Fidelity, Wi-Fi, or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within the network node 1100.

Processing circuitry 1112 is configured to perform any determining, calculating, or similar operations (e.g., certain obtaining operations) described herein as being provided by a network node . These operations performed by processing circuitry 1112 may include processing information obtained by processing circuitry 1112 by, for example, converting the obtained information into other information, comparing the obtained information, or converted information to information stored in the network node, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination.

Processing circuitry 1112 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and/or encoded logic operable to provide, either alone or in conjunction with other network node 1100 components, such as device readable medium, computer ,1100 functionality. For example, processing circuitry 1112 may execute instructions stored in device readable medium 1115 or in memory within processing circuitry 1112. Such functionality may include providing any of the various wireless features, functions, or benefits discussed herein. In some embodiments, processing circuitry 1112 may include a system on a chip.

In some embodiments, processing circuitry 1112 may include one or more of radio frequency, RF, transceiver circuitry and baseband processing circuitry. In some embodiments, RF transceiver circuitry and baseband processing circuitry may be on separate chips or sets of chips, boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry and baseband processing circuitry may be on the same chip or set of chips, boards, or units.

In certain embodiments, some or all the functionality described herein as being provided by a network node may be performed by the processing circuitry 1112 executing instructions stored on device readable medium 1115 or memory within processing circuitry 1112. In alternative embodiments, some or all the functionalities may be provided by processing circuitry 1112 without executing instructions stored on a separate or discrete device readable medium, such as in a hard-wired manner. In any of those embodiments, whether executing instructions stored on a device readable storage medium or not, processing circuitry 1112 can be configured to perform the described functionality. The benefits provided by such functionality are not limited to processing circuitry 1112 alone or to other components of network node but are enjoyed by network node 1100 and/or by end users.

Device readable medium or memory 1115 may comprise any form of volatile or non-volatile computer readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non-transitory device readable and/or computerexecutable memory devices that store information, data, and/or instructions that may be used by processing circuitry 1112. Device readable medium 1115 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, etc. and/or other instructions capable of being executed by processing circuitry 1112 and, utilized by network node. Device readable medium may be used to store any calculations made by processing circuitry 1112 and/or any data received via interface 1104. In some embodiments, processing circuitry 1112 and device readable medium 1115 may be considered to be integrated.

The communications interface 1104 is used in the wired orwireless communication of signaling and/or data between network node, 1100 and other nodes. Interface 1104 may comprise port(s)/terminal(s) to send and receive data, for example to and from network node ,1100 over a wired connection. Interface 1104 also includes radio front end circuitry that may be coupled to, or in certain embodiments a part of, an antenna. Radio front end circuitry may comprise filters and amplifiers. Radio front end circuitry may be connected to the antenna and/or processing circuitry 1112.

Examples of a network node 1100 include, but are not limited to an gNB, a gateway, a smart phone, a mobile phone, a cell phone, a voice over IP (VoIP) phone, a wireless local loop phone, a tablet computer, a desktop computer, a personal digital assistant (PDA), a wireless cameras, a gaming console or device, a music storage device, a playback appliance, a wearable terminal device, a wireless endpoint, a mobile station, a tablet, a laptop, a laptop-embedded equipment (LEE), a laptop-mounted equipment (LME), a smart device, a wireless customer-premise equipment (CPE), a vehicle-mounted wireless terminal device, a drone, an O-CU (O-RAN Central Unit), an O-DU (O-RAN Distributed Unit), an O-RU (O-RAN Radio Unit), a Near-RT RIC (Near Real-Time RAN Intelligent Controller), a Non-RT RIC, SMO (Service Management and Orchestration) etc.

The communication interface 1104 may encompass wired and/or wireless networks such as a local-area network (LAN), a wide-area network (WAN), a computer network, a wireless network, a telecommunications network, another like network or any combination thereof. The communication interface may be configured to include a receiver and a transmitter interface used to communicate with one or more other devices over a communication network according to one or more communication protocols, such as Ethernet, TCP/IP, SONET, ATM, optical, electrical, and the like). The transmitter and receiver interface may share circuit components, software, or firmware, or alternatively may be implemented separately.

In embodiments, the UE 110 may comprise all of the features described in relation to Fig. 11 , or a subset of the features described in relation to Fig. 11 . In embodiments, The UE comprises a power supply circuitry configured to supply power to the processor/processing circuitry.

In embodiments, the AP 120 may comprise all of the features described in relation to Fig. 11 , or a subset of the features described in relation to Fig. 11. In embodiments, The AP comprises a power supply circuitry configured to supply power to the processor/processing circuitry.

According to one aspect of the present disclosure, a node in a radio network is provided. The node comprises a processor and a memory, the memory containing instructions executable by the processor whereby the node is operative to: generate reference symbol sequences P for a time interval by obtaining required number of reference symbol sequences K for the time interval, obtaining an orthogonality metric c, obtaining allocated pilot resources R and generating reference symbol sequences P using the required number of reference sequences K, the orthogonality metric c and the allocated pilot resources R, allocate the generated reference symbol sequences P to a radio access node and a user equipment, UE, initiate transmission of a signal between the radio access node and the UE. Additionally, or alternatively, the node is further operable to generate the reference symbol sequences P by combining a first set of binary sequences and a second set of binary sequences.

Additionally, or alternatively, the first set of binary sequences have a first number n of members, wherein the members have a length k, wherein positions within the binary sequences being allocated a value of one coincide in at most a second number A of positions. ,

Additionally, or alternatively, the second set of binary sequences have a unit norm of the length k and an orthogonality metric c less or equal than a threshold equal to a fraction defined as the second number of A positions divided by the length k.

Additionally, or alternatively, the first set of binary sequences are generated as difference sets defined by the first number n, the length k, and second number A of positions.

Additionally, or alternatively, the difference sets are defined as:

Additionally, or alternatively, the difference set is adapted to a target length of reference symbols by deleting columns of the difference sets.

Additionally, or alternatively, the difference set is adapted to a target number of members m by deleting rows of the difference set, where in the first set of binary sequences are generated as extended difference sets defined by the first number n, the length k, the second number A of positions, and the target number of members m.

According to one aspect of the present disclosure, a UE in a radio network is provided, the user device comprising: a processor, and a memory, said memory containing instructions executable by said processor, whereby said user device is operative to perform the methods described herein.

Fig. 12 illustrate functional modules of a network node 1100 according to the present disclosure. The network node comprises:

A generation module 1210 configured to generate reference symbol sequences P for a time interval by obtaining required number of reference symbol sequences K for the time interval, obtaining an orthogonality metric c, obtaining allocated pilot resources R and generating reference symbol sequences P using the required number of reference sequences K, the orthogonality metric c and the allocated pilot resources R.

An allocation module 1220 configured to allocate the generated reference symbol sequences P to a radio access node and a user equipment, UE.

An initialization module 1230 configured to initiate transmission of a signal between the radio access node and the UE.

Fig. 13 shows functional modules of a UE 110 according to one or more embodiments of the present disclosure. The UE comprising: A reception module 1310 configured to receive a control signal indicative of generated reference symbol sequences (P).

A transmission module 1320 configured to transmit to a radio access node 120 or receiving from a radio access 120 node using the received reference symbol sequences P.

Finally, it should be understood that the disclosure is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1. A node in a radio network, the node comprising a processor and a memory, the memory containing instructions executable by the processor whereby the node is operative to: generate reference symbol sequences (P) for a time interval by obtaining required number of reference symbol sequences (K) for the time interval, obtaining an orthogonality metric (c), obtaining allocated pilot resources (R) and generating reference symbol sequences (P) using the required number of reference sequences (K), the orthogonality metric (c) and the allocated pilot resources (R), allocate the generated reference symbol sequences (P) to a radio access node and a user equipment, UE, initiate transmission of a signal between the radio access node and the UE.

2. The node according to claim 1 , wherein the node is further operable to: generate the reference symbol sequences (P) by combining a first set of binary sequences and a second set of binary sequences, wherein the first set of binary sequences have a first number (n) of members, wherein the members have a length (fc), wherein positions within the binary sequences being allocated a value of one coincide in at most a second number ( ) of positions, wherein the second set of binary sequences have a unit norm of the length (fc) and an orthogonality metric (c) less or equal than a threshold equal to a fraction defined as the second number of ( ) positions divided by the length (fc).

3. The node according to claim 2, where in the first set of binary sequences are generated as difference sets defined by the first number (n), the length (fc), and second number ( ) of positions.

4. The node according to claim 3, wherein the difference sets are defined as:

5. The node according to claim 4, wherein the difference set is adapted to a target length of reference symbols by deleting columns of the difference sets.

6. The node according to any of claims 3-5, wherein the difference set is adapted to a target number of members (m) by deleting rows of the difference set, where in the first set of binary sequences are generated as extended difference sets defined by the first number (n), the length (fc), the second number ( ) of positions, and the target number of members (m).

7. A computer-implemented method performed by a node in a radio network (100), the method comprising: generating reference symbol sequences (P) for a time interval by obtaining required number of reference sequences (K) for the time interval, obtaining an orthogonality metric (c), obtaining allocated pilot resources (R) and generating reference symbol sequences (P) using the required number of reference symbol sequences (K), the orthogonality metric (c) and the allocated pilot resources (P), allocating the generated reference symbol sequences (P) to a radio access node and a user equipment, UE, initiating transmission of a signal between the radio access node and the UE.

8. The method according to claim 7, wherein generating reference symbol sequences

(P) comprises: combining a first set of binary sequences and a second set of binary sequences, wherein the first set of binary sequences have a first number (n) of members, wherein the members have a length (fc), wherein positions within the binary sequences being allocated a value of one coincide in at most a second number ( ) of positions, wherein the second set of binary sequences have a unit norm of the length (fc) and an orthogonality metric (c) less or equal than a threshold equal to a fraction defined as the second number of ( ) positions divided by the length (fc).

9. The method according to claim 8, where in the first set of binary sequences are generated as difference sets defined by the first number (n), the length (fc), and second number ( ) of positions.

10. The method according to claim 9, wherein the difference sets are defined as:

11 . The method according to claim 10, wherein the difference set is adapted to a target length of reference symbols by deleting columns of the difference sets.

12. The method according to any of claims 10-11 , wherein the difference set is adapted to a target number of members (m) by deleting rows of the difference set, where in the first set of binary sequences are generated as extended difference sets defined by the first number (n), the length (fc), the second number ( ) of positions, and the target number of members (m).

13. A method performed by a user equipment UE, the method comprising: receiving a control signal indicative of generated reference symbol sequences transmitting to a radio access node or receiving from a radio access node using the received reference symbol sequences (P).

14. The method according to claim 13, the method further comprises providing user data; and forwarding the user data to a host via the transmission to the network node.

15. A user equipment, UE, in a radio network, the user device comprising: a processor, and a memory, said memory containing instructions executable by said processor, whereby said user device is operative to perform the method according to any of claims 13-14.

16. A host configured to operate in a communication system to provide an over-the- top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps: receive a control signal indicative of generated reference symbol sequences (P), transmit to a radio access node or receiving from a radio access node using the received reference symbol sequences (P), to receive the user data from the host.

17. The host of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE to transmit the user data to the UE from the host.

18. The host of any of claims 16-17, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

19. A method implemented by a host operating in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the UE performs any of the steps: receiving a control signal indicative of generated reference symbol sequences (P), transmitting to a radio access node or receiving from a radio access node using the received reference symbol sequences (P), to receive the user data from the host.

20. The method according to claim 19, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

21 . The method according to claim 20, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

22. The method according to claim 21 , further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application.

23. A host configured to operate in a communication system to provide an over-the- top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a network node in a cellular network for transmission to a user equipment (UE), the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to: generate reference symbol sequences (P) for a time interval by obtaining required number of reference sequences (K) for the time interval, obtaining an orthogonality metric (c), obtaining allocated pilot resources (R) and generating reference symbol sequences (P) using the required number of reference symbol sequences (K), the orthogonality metric (c) and the allocated pilot resources (P), allocate the generated reference symbol sequences (P) to a radio access node and a user equipment, UE, initiate transmission of a signal between the radio access node and the UE, to transmit the user data from the host to the UE.

24. The host according to claim 23, wherein: the processing circuitry of the host is configured to execute a host application that provides the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application to receive the transmission of user data from the host.

25. A method implemented in a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the network node isa operable to: process circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a network node in a cellular network for transmission to a user equipment (UE), the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to: generating reference symbol sequences (P) for a time interval by obtaining required number of reference sequences (K) for the time interval, obtaining an orthogonality metric (c), obtain allocated pilot resources (R) and generating reference symbol sequences (P) using the required number of reference symbol sequences (K), the orthogonality metric (c) and the allocated pilot resources (P), allocating the generated reference symbol sequences (P) to a radio access node and a user equipment, UE, initiating transmission of a signal between the radio access node and the UE, to transmit the user data from the host to the UE.

26. The method according to claim 25, further comprising, at the network node, transmitting the user data provided by the host for the UE.

27. The method according to any of claims 25-26, wherein the user data is provided at the host by executing a host application that interacts with a client application executing on the UE, the client application being associated with the host application.