Apparatus for integrated sensing and communication

Abstract

Apparatus is disclosed for transmitting, receiving or both transmitting and receiving a series of different positioning reference signals (PRSs), each having a pseudo-random symbol sequence, wherein t

Description

Field of the Invention Various example embodiments relate to apparatus for Integrated Sensing and Communication, ISAC, and to corresponding methods, computer programs and computer readable media for the same. Background to the Invention ISAC refers to combining sensing and communication systems such that, for example, a network can detect reflections of communications signals from objects in the environment in order to estimate parameters of objects (e.g., range, velocity, angle). In the case of mono-static sensing with a co-located transmitter and sensing receiver (configurations a and c in figure 1, where the device is both sounder and sensor), complete knowledge of the transmitted modulation symbols can be assumed at the sensing receiver. However, in the case of bi-static sensing where the transmitter and sensing receiver are not co-located (configurations b, d, e and f in figure 1 with a separate sounder and sensor), usually only dedicated reference / pilot symbols are used for sensing. Summary of the Invention According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. Brief Description of Drawings Figure 1 illustrates different configurations for Integrated Sensing and Communication, ISAC; Figures 2A and 2B illustrate exemplary Positioning Reference Signal, PRS, configurations; Figure 3 illustrates exemplary time domain configuration of a PRS resource; Figures 4 and 5 are periodograms illustrating PRS distortion; Figure 6 illustrates an exemplary PRS configuration; Figure 7 illustrates an autocorrelation function of PRS of figure 6 over time; Figure 8 illustrates a cyclic shift of a PRS; Figure 9 is a message sequence diagram illustrating ISAC with PRSs; Figure 10 is a simplified block diagram illustrating a device that is suitable for implementing aspects of the present disclosure illustrated in figures 1 to 9. Detailed Description The principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these example embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below. The terminology used herein to describe embodiments is not intended to limit the scope. The articles ‘a,’ ‘an,’ and ‘the’ are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms ‘comprises,’ ‘comprising,’ ‘includes,’ and / or ‘including,’when used herein, specify the presence of stated features, items, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and / or groups thereof. Unless otherwise defined, all terms (includingtechnical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein. It is known to use Position Reference Signals, PRSs, for ISAC. Position Reference Signals are described in clause 7.4.1.7 of 3GPP Technical Standard (TS) 38.211 (3GPP TS 38.211, “NR; Physical channels and modulation,” Technical Specification (TS) 38.211, 2025, version 19.1.0). In particular, the following two configuration parameters define the structure of PRS resources in a Physical Resource Block (PRB): ■ comb size which can be selected from the set K"cpOmb e (2,4,6,12} (clause 7.4.1.7.3 of TS38.211). The chosen specifies how densely the PRS resources are allocated within a resource set, i.e., every K^b"^ resource element (RE) is allocated for PRS. ■ size of the PRS resource in time domain LPRS, which can have values LPRS e {1,2,4,6,12} (clause 7.4.1.7.3 of TS38.211) and defines over how many OFDM symbols per slot the PRS resource extends in time domain. For example, figures 2A and 2B shows two different PRS allocation configurations with {LPRS = 6, K^b = 6} (left) and {LPRS = 12,Kp^b = 12} (right) for one slot and one PRB, where the x-axis represents OFDM symbols (time) and the y-axis subcarriers (frequency). Note that not all combinations of {Lprs, K^b) are possible, but only the ones specified in clause 7.4.1.7.3 of TS38.211. Further, 1™^ defines the first OFDM symbol with PRS within the slot and kp^et e {0,1,..., Kp^b _ 1} the RE offset. Different options for those parameters are shown in Fig. 1 as well. In TS 38.214 (3GPP, “NR; Physical layer procedures for data,” Technical Specification (TS) 38.214, 2025, version 19.1.0), parameter dl-PRS-ResourceBandwidth defines the number of PRBs configured for DL PRS transmission. Currently, the parameter has a granularity of PRBs, and it is possible to configure a minimum and maximum bandwidth of 24 and 272 PRBs, respectively. Clause 7.4.1.7 of TS 38.211 specifies how PRS sequences are generated and how PRS resources are mapped to slots. Firstly, clause 7.4.1.7.2 specifies that the reference-signal sequence r(m) is defined by / nrRO _ ?22 |D>seq init 1024 1 1 r(m) =-(1- 2c(2m)) + j — (1 - 2c(2m + 1)) v2 v2 where the pseudo-random sequence c(i) is defined in clause 5.2.1. The pseudo-random sequence generator shall be initialised with + 2“(NXb<f + 1 + 1)(2(n™Ieq mod 1024) + 1) + (n^ mod 1024)^ mod 231 where npf is the slot number, the downlink PRS sequence IDnpDR|eq e {0,1, ...,4095} is given by the higher-layer parameter dl-PRS-SequencelD, and 1 is the OFDM symbol within the slot to which the sequence is mapped. As we will explain in the next section, npf is of particular importance, as it represents the slot number within a frame. Therefore, it causes the sequences of PRS resources spanning multiple frames to repeat after each frame. Furthermore, clause 7.4.1.7.3 describes how PRS resources are mapped to slots. Fig. 3 shows an example of this with a single PRS resource and the following parameters: ■ periodicity TpeRS: defines the slot periodicity of the PRS resource set. ■ slot offset Topffsset: specifies the offset in slots of the PRS resource set. ■ repetition factor TrPpS: defines how often the PRS resource is repeated. ■ time gap Tjaps: specifies the offset between consecutive PRS resources. Moreover, Tpffssetres allows to offset each PRS resource relative to Tpffsset. In Fig. 4, only a single PRS resource with Tpffssetres = 0 is shown for simplicity. It is further worth mentioning that different options for muting DL PRS resources in certain slots can be configured, i.e., for muting PRS resources in time domain. Importantly, the inventors have appreciated an aspect of existing PRS usage which is detrimental to ISAC performance. In this regard, figures 4 and 5 are periodograms illustrating distortion in respect of power spectral density against range and speed of a sensed object. Figure 4 illustrates real ISAC measurements recorded where the transmit signal of a sensing burst spanned multiple frames and repeated after each frame. From the periodogram, obtained after processing the channel state information (CSI) matrix with conventional Fourier-based processing, undesired vertical distortion lines, for example, as marked 40, spaced by 0.54 m / s in the speed / Doppler domain (the x-axis), can clearly be observed (in particular, see the circled area indicated). Note that there are even stronger distortions around + / - 4.5 m / s. However, these can be attributed to time domain holes caused by empty uplink, UL, symbols due to Time Division Duplexing, TDD, transmission. Also, 4 although the distortion lines spaced by 0.54 m / s are not as severe as the TDD-induced artifacts, they are not negligible and can still mask weak targets in the periodogram and prevent their detection. In general, non-linearities, e.g., due to power amplifiers, PAs, cause distortions in the periodogram and raise the overall noise floor. In case of repeating signals, the distortions appear at well-defined locations in the periodogram, which are determined by the periodicity of the signal in time. In particular, the spacing of the distortions in the speed / Doppler domain can be computed as: △Vdis= frep.(Co / 2fc) ~ 0.54 m / s where: frep is the repetition frequency of the signal, in this case where frep = 1 / Trep (1 / 10ms or 100Hz) with Trep being the repetition interval corresponding to a frame duration of 10 ms, Co is the speed of light, and fc is the carrier frequency, in this case, 27.6GHz. As can be seen from figure 4, AvdiS = 0.54 m / s, corresponding to the spacing of the distortion lines in the periodogram. For comparison, figure 5 shows a periodogram obtained with the sensing signal only spanning a single frame, therefore exhibiting no repetitions. In particular, if one observed the circled areas indicated in both figures 4 and 5, one can clearly observe that the more prominent vertical Doppler distortion lines in figure 4 that are not present in figure 5 case so that the previously mentioned TDD-induced artifacts are the only substantially observed impairments. Accordingly, the inventors have appreciated that an ideal signal for sensing should not exhibit temporal correlations which is not currently the case for PRS. Indeed, figure 6 shows a PRB of an example PRS configuration generated with MATLAB’s 5G toolbox using a comb size = 2 (i.e., every 2nd subcarrier allocated) and spanning LpRS= 12 OFDM symbols per slot. Configuring this PRS resource to be transmitted every slot allows to obtain the dense allocation necessary to achieve a high processing gain (and thus SNR), as well as high values for unambiguous range and speed. To further emphasize the above, figure 7 illustrates an autocorrelation function of a conventional PRS signal over time (averaged over all subcarriers), and reveals strong correlation peaks not only at zero lag, but also at multiples of the frame duration (1120 OFDM symbols). This suggests a repetition of the PRS signal at the frame level which is verified by OFDM symbol #1 (first symbol of the first frame) with OFDM symbol #1121 (first symbol of the second frame) being identical. As already above, this is due to the pseudo-random sequence generator being initialized based on the slot number within a frame which resets after each frame. Accordingly, with the inventors’ appreciation that an ideal signal for sensing should not exhibit temporal correlations, apparatus of a first embodiment is provided comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to at least: transmit, receive or both transmit and receive a series of different Positioning Reference Signals, PRSs, each having a pseudo-random symbol sequence, wherein the series is configured so as to not repeat over adjacent signal frames. In one implementation, the pseudo-random symbol sequence may be based at least in part on a parameter which is continuous across at least some frame boundaries, for example, a system frame number. In another implementation, the apparatus may be further caused to: perform an active measure to prevent the series repeating over adjacent signal frames, the active measure being at least one of: changing the pseudo-random symbol sequence; changing the pseudo-random symbol sequence at a frame boundary; changing a modulation symbol; and changing a modulation symbol at a frame boundary, wherein repetition of the series would otherwise occur but for the active measure. Pseudo-random symbol sequence change may be implemented by at least one of: initializing a new pseudo-random symbol sequence with a different initializing parameter than one previously used; and initializing a new pseudo-random symbol sequence with an initializing parameter which is shifted or scrambled relative to one previously used. Also, a modulation symbol change may be implemented by at least one of: using a modulation symbol which is different from that previously used; and using a modulation symbol which is phase shifted relative to that previously used. Change may be implemented by Radio Resource Control, RRC, between a network and User Equipment, UE. For example, the implemented change may be to a PRS sequence identifier, ID. In respect of both the first and second embodiments, the apparatus may be caused to either transmit or receive the series of PRSs for mono-static, bi-static or multi-static integrated sensing and communication (ISAC). Moreover, the apparatus may be further caused to: either transmit or receive a signal indicating the configuration of the series of PRSs to co-ordinate mono-static, bi-static or multistatic ISAC with external apparatus. Also, the apparatus may be caused to both transmit and receive the series of PRSs for mono-static ISAC. Furthermore, the apparatus may be for either a network or a User Equipment, UE, apparatus. Initializing random sequence generation with an absolute slot number instead of a relative slot number within a frame In respect of the first embodiment describe above, the pseudo-random symbol sequence is based at least in part on a parameter which is continuous across at least some frame boundaries, for example, a system frame number. As mentioned above, pseudo-random sequences for PRS are generated with an initializing parameter cinit: / PRS Cinit = 222 + 210(Ns%<f + I + 1)(2(¾ mod 1024) + 1) 1 1UZ4- + (niDRIeq mod 1024)^ mod 231 where is the slot number within the frame, causing the pseudo-random sequences to repeat after each frame. One option to circumvent this is to have an absolute slot counter exceeding frame 6 boundaries. This could be achieved by using the System Frame Number (SFN) as defined in 3GPP, “NR; Radio Resource Control (RRC) "Technical Specification (TS) 38.331,2025, version 19.1.0. The SFN is a 10-bit number e {0,..., 1023}. One could account for the SFN when incrementing the slot number, e.g., by defining a system slot number n$. Using n$ instead of forcinit would enable PRS sequences to only repeat after 1024 frames, i.e. after 1024x 10 ms = 10.24 s, which is more than sufficient for a sensing burst. Note that in the bi- or multi-static case, n$ would have to be signaled to neighboring gNBs acting as potential sensing RXs. Changing sequence ID for each frame via Radio Resource Control (RRC) signaling In respect of the second embodiment describe above, the initialization of cinit could be adapted by changing the PRS sequence ID n^^q e {0,1, ...,4095}. This could be achieved via RRC signaling whereby gNB shall reserve a set of PRS sequence IDs as (nf^ nf™ 2, ••• which is indicated in RRS signaling. For sensing operation, one PRS sequence ID is selected from the ID set, sequentially. Also here, the high number of different npDRfeq would allow sufficiently long sensing bursts that are uncorrelated over time. Cyclically shifting sequences at each frame with respect to the previous one Alternatively, in respect of the second embodiment describe above, cyclical shifting may be employed. For example, quadrature phase-shift keying (QPSK) modulation symbols that constitute the PRS may be cyclically shifted along the subcarrier axis in each frame with respect to the previous one. For this purpose, a parameter such as the SFN could be used to determine the number of elements by which the PRS QPSK symbols are cyclically shifted. Converting the SFN from binary to decimal and focusing on a single OFDM symbol at the same position in three consecutive frames with the same PRS configuration, figure 8 illustrates how a cyclic shift can be applied to make the sensing burst comprising multiple frames uncorrelated for Doppler processing. In this figure, (N — / CoffsetV^Tomb's the total QPSK symbols of the PRS present in the OFDM symbol that has a total of N subcarriers. If a larger number of frames than (N — / Coffset) / ^cPomb _ 1 is used, another strategy to define cyclic shifts than the linearly increasing one in figure 8 must be adopted. One possibility would be using different cyclic shifts within each frame, instead of a constant cyclic shift throughout the whole frame as in the considered example. Sharing change information with bistatic and multi-static ISAC As mentioned above, in the case of mono-static sensing with a co-located transmitter and sensing receiver (configurations a and c in figure 1), complete knowledge of the transmitted symbols can be assumed at the sensing receiver. Accordingly, a measure taken by a transmitter to provide temporally uncorrelated reference signal transmissions for sensing would be known by the receiver. In the case of bistatic and multi-static sensing where the transmitter and sensing receiver are not co-located 7 (configurations b, d, e and f in figure 1), a measure taken by a transmitter to provide temporally uncorrelated reference signal transmissions for sensing would have to be conveyed to the receiver. For example, figure 9 is a message sequence diagrams illustrating User Equipment, UE, a network node, gNB, core network elements providing a Location Management Function, LMF, and a Sensing Management Function, SeMF, and a Sensing Receiver, SRX. Although only individual UE and SRX is shown, the signaling of the gNB and LMF / SeMF may be provided to multiple UE and SRXs.The illustrated signaling is as follows: Step 900: Select PR Symbol Sequence Change. A core network LMF or SeMF selects a PR symbol sequence change scheme to be applied to PRS signals at frame boundaries. Step 901: Request PRS. The core network LMF or SeMF requests a non-repeating PRS optimized for sensing with the selected PR symbol sequence change scheme. In a first option: Step 902: Provide PSSS Change. The LMF / SeMF signals the PR symbol sequence change scheme to the gNB which in turn signals the same to the UE Step 903: Provide PSSS Change. The LMF / SeMF signals the PR symbol sequence change scheme to the SRX. In a second option: Step 902’: Provide PSSS Change. The LMF / SeMF signals the PR symbol sequence change scheme to the gNB. Step 903’: Provide PSSS Change. In turn, the gNB signals the PR symbol sequence change scheme to the UE and the SRX. Continuing: Step 904: The PRS (with selected PR symbol sequence change scheme) is signaled to UE. Step 905: The PRS (with selected PR symbol sequence change scheme) is also signaled to SRX. Step 906: UE decodes the PRS. Step 907: SRX senses the PRS for performing ISAC with the uncorrelated PRS increasing the probability of detecting true targets and reduces the probability of detecting false targets / impulsive sidelobes. In summary, the above provides technical solutions for achieving the technical effect of enabling temporally uncorrelated reference signal transmissions for sensing, allowing to achieve a better sensing performance by reducing the distortions in the periodogram. Whilst described using the example of PRS of 3GPP Technical Standards for gNB-based DL sensing, the proposals could in principle be applied to other reference signals, e.g., SRS for UE-based UL sensing, and other communications standards. To the extent that such other reference signals are used for ISAC positioning, they too can be considered PRSs for the purposes of the present application. The apparatus described above may be alternatively characterized by the underlying methods including by a first method comprising transmitting, receiving or both transmitting and receiving a series of different Positioning Reference Signals, PRSs, each having a pseudo-random symbol sequence, wherein the series is configured so as to not repeat over adjacent signal frames. In one implementation, the pseudo-random symbol sequence may be based at least in part on a parameter which is continuous across at least some frame boundaries, for example, a system frame number. In another implementation, the method may further comprise: performing an active measure to prevent the series repeating over adjacent signal frames, the active measure being at least one of: changing the pseudo-random symbol sequence; changing the pseudo-random symbol sequence at a frame boundary; changing a modulation symbol; and changing a modulation symbol at a frame boundary, wherein repetition of the series would otherwise occur but for the active measure. Pseudo-random symbol sequence change may be implemented by at least one of: initializing a new pseudo-random symbol sequence with a different initializing parameter than one previously used; and initializing a new pseudo-random symbol sequence with an initializing parameter which is shifted or scrambled relative to one previously used. Also, a modulation symbol change may be implemented by at least one of: using a modulation symbol which is different from that previously used; and using a modulation symbol which is phase shifted relative to that previously used. Change may be implemented by Radio Resource Control, RRC, between a network and User Equipment, UE. For example, the implemented change may be to a PRS sequence identifier, ID. In respect of both the first and second methods, the method may further comprise either transmitting or receiving the series of PRSs for mono-static, bi-static or multi-static integrated sensing and communication (ISAC). Moreover, the method may be further comprise: either transmitting or receiving a signal indicating the configuration of the series of PRSs to co-ordinate mono-static, bi-static or multistatic ISAC with external apparatus. The method may comprise both transmitting and receiving the series of PRSs for mono-static ISAC. The method may be for either a network or user equipment, UE, apparatus. Furthermore, corresponding non-transitory computer readable medium may be provided comprises program instructions that, when executed by an apparatus, cause the apparatus to perform at least such a method. Similarly, a corresponding computer program may be provided comprising instructions, which, when executed by an apparatus, cause the apparatus to perform at least such a method. The apparatus of the first embodiment described above may alternative be characterized by apparatus comprising: means for transmitting, receiving or both transmitting and receiving a series of different Positioning Reference Signals, PRSs, each having a pseudo-random symbol sequence, wherein the series is configured so as to not repeat over adjacent signal frames. In one implementation, the pseudo-random symbol sequence may based at least in part on a parameter which is continuous across at least some frame boundaries, for example, a system frame number. In another implementation, the apparatus may further comprise: means for performing an active measure to prevent the series repeating over adjacent signal frames, the active measure being at least one of: changing the pseudo-random symbol sequence; changing the pseudo-random symbol sequence at a frame boundary; changing modulation symbol; and changing modulation symbol at a frame boundary, wherein repetition of the series would otherwise occur but for the active measure. Pseudo-random symbol sequence change may be implemented by at least one of: means for initializing a new pseudo-random symbol sequence with a different initializing parameter than one previously used; and means for initializing a new pseudo-random symbol sequence with an initializing parameter which is shifted or scrambled relative to one previously used. Also, modulation symbol change may be implemented by at least one of: means for using a modulation symbol which is different from that previously used; and means for using a modulation symbol which is phase shifted relative to that previously used. Change may be implemented by Radio Resource Control, RRC, between a network and User Equipment, UE. For example, the implemented change may be to a PRS sequence identifier, ID. In respect of both the third and fourth embodiments, the apparatus may further comprise either means to transmit or means to receive the series of PRSs for mono-static, bi-static or multi-static integrated sensing and communication (ISAC). Moreover, the apparatus may further comprise: either means to transmit or means to receive a signal indicating the configuration of the series of PRSs to co-ordinate mono-static, bi-static or multi-static ISAC with external apparatus. The apparatus may further comprise means to both transmit and receive the series of PRSs for mono-static ISAC. Also, the apparatus may be for either a network or user equipment, UE, apparatus. The apparatus of the first embodiment described above may alternative be characterized by apparatus comprising: communications circuitry configured to transmit, receive or both transmit and receive a series of different Positioning Reference Signals, PRSs, each having a pseudo-random symbol sequence, wherein the series is configured so as to not repeat over adjacent signal frames. In one implementation, the pseudo-random symbol sequence may based at least in part on a parameter which is continuous across at least some frame boundaries, for example, a system frame number. In another implementation, the apparatus may further comprise: control circuitry configured to performing an active measure to prevent the series repeating over adjacent signal frames, the active measure being at least one of: changing the pseudo-random symbol sequence; changing the pseudorandom symbol sequence at a frame boundary; changing modulation symbol; and changing modulation symbol at a frame boundary, wherein repetition of the series would otherwise occur but for the active measure. Pseudo-random symbol sequence change may be implemented by at least one of: sequence circuitry configured to initialize a new pseudo-random symbol sequence with a different initializing parameter than one previously used; and sequence circuitry configured to for initializing a new pseudo-random 10 symbol sequence with an initializing parameter which is shifted or scrambled relative to one previously used. Also, modulation symbol change may be implemented by at least one of: modulation circuitry configured to use a modulation symbol which is different from that previously used; and modulation circuitry configured to use a modulation symbol which is phase shifted relative to that previously used. Change may be implemented by Radio Resource Control, RRC, between a network and User Equipment, UE. For example, the implemented change may be to a PRS sequence identifier, ID. In respect of both the fifth and sixth embodiments, The apparatus may further comprise either integrated sensing and communication, ISAC, circuitry configured to transmit or ISAC circuitry configured to receive the series of PRSs for mono-static, bi-static or multi-static ISAC. Moreover, the apparatus may further comprise: either ISAC circuitry configured to transmit or ISAC circuitry configured to receive a signal indicating the configuration of the series of PRSs to co-ordinate monostatic, bi-static or multi-static ISAC with external apparatus. The apparatus may further ISAC circuitry configured to both transmit and receive the series of PRSs for mono-static ISAC. The apparatus may be for either a network or user equipment, UE, apparatus. Figure 10 is a simplified block diagram of a device 1000 that is suitable for implementing example embodiments of the present disclosure. As shown, the device 1000 includes a processor 1010, a memory 1020 coupled to the processor 1010, a communication module 1030 coupled to the processor 1010, and a communication interface (not shown) coupled to the communication module 1030. The memory 1020 stores at least a program 1040. The communication module 1030 is for bidirectional communications, for example, via multiple antennas. The communication interface may represent any interface that is necessary for communication. The program 1040 is assumed to include program instructions that, when executed by the associated processor 1010, enable the device 1000 to operate in accordance with the example embodiments of the present disclosure, as discussed herein with reference to figures 1-9. The example embodiments herein may be implemented by computer software executable by the processor 1010 of the device 1000, or by hardware, or by a combination of software and hardware. The processor 1010 may be configured to implement various example embodiments of the present disclosure. The memory 1020 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1020 is shown in the device 1000, there may be several physically distinct memory modules in the device 1000. The processor 1010 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1000 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. 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 analog, digital and / or quantum circuitry) and (b) combinations of hardware circuit(s) and software, such as (as applicable): (i) a combination of analog, digital and / or quantum hardware circuit(s) with software / firmware and (ii) any or all portions of hardware processor(s) (including digital and / or quantum processor(s)) with software, and memory(ies) that work together to cause an apparatus, such as a mobile device, computing device, or server, to perform various functions) and (c) any or all portions of hardware circuit(s), such as microprocessor(s), processor(s) and / or quantum processor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. Generally, various example embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of example 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. The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computerexecutable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carryout the methods of figures 5 and 6. 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 example 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. 12 Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server. In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable media. 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 readonly memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), Digital Versatile Disc (DVD), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. Various example embodiments of the techniques have been described. In addition to or as an alternative to the above, the following examples are described. The features described in any of the following examples may be utilized with any of the other examples described herein. List of abbreviations 3GPP 3rd Generation Partnership Project CSI Channel State Information DL DownLink gNB Next Generation (5G) Node B I SAC Integrated Sensing and Communication OFDM Orthogonal Frequency-Division Multiplexing PA Power Amplifier PoC Proof of Concept PRB Physical Resource Block PRS Positioning Reference Signal QPSK Quadrature Phase-Shift Keying RE Resource Element RRC Radio Resource Control SFN System Frame Number SINR Signal-to-interference-plus-noise ratio SRS Sounding Reference Signal UE User Equipment UL Uplink

Claims

1. Apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to at least:transmit, receive or both transmit and receive a series of different Positioning Reference Signals, PRSs, each having a pseudo-random symbol sequence, wherein the series is configured so as to not repeat over adjacent signal frames.

2. Apparatus as claimed in claim 1, wherein the pseudo-random symbol sequence is based at least in part on a parameter which is continuous across at least some frame boundaries.

3. Apparatus as claimed in claim 2, wherein the parameter is a system frame number.

4. Apparatus as claimed in claim 1, further caused to:perform an active measure to prevent the series repeating over adjacent signal frames, the active measure being at least one of:changingthe pseudo-random symbol sequence;changingthe pseudo-random symbol sequence at a frame boundary;changing a modulation symbol; andchanging a modulation symbol at a frame boundary, wherein repetition of the series would otherwise occur but for the active measure.

5. Apparatus as claimed in claim 4, further caused to implement pseudo-random symbol sequence change by at least one of:initializing a new pseudo-random symbol sequence with a different initializing parameter than one previously used; andinitializing a new pseudo-random symbol sequence with an initializing parameter which is shifted or scrambled relative to one previously used.

6. Apparatus as claimed in claim 4, further caused to implement a modulation symbol change by at least one of:using a modulation symbol which is different from that previously used; andusing a modulation symbol which is phase shifted relative to that previously used.

7. Apparatus as claimed in any of claims 4-6, further caused to:implement change by Radio Resource Control, RRC, between a network and User Equipment, UE.

8. Apparatus as claimed in claim 7, wherein the implemented change is to a PRS sequence identifier, ID.

9. Apparatus according to any preceding claim, caused to either transmit or receive the series of PRSs for mono-static, bi-static or multi-static integrated sensing and communication (ISAC).

10. Apparatus accordingto claim 9, further caused to:either transmit or receive a signal indicating the configuration of the series of PRSs to co-ordinate mono-static, bi-static or multi-static ISAC with external apparatus.

11. Apparatus accordingto any of claims 1-8, caused to both transmit and receive the series of PRSs for mono-static ISAC.

12. Apparatus accordingto any preceding claim for either a network or a User Equipment, UE.

13. A method comprising transmitting, receiving or both transmitting and receiving a series of different PRSs, each having a pseudo-random symbol sequence, wherein the series is configured so as to not repeat over adjacent signal frames.

14. A method accordingto claim 13, wherein the pseudo-random symbol sequence is based at least in part on a parameter which is continuous across at least some frame boundaries.

15. A method accordingto claim 14, wherein the parameter is a system frame number.

16. A method accordingto claim 13, further comprising:performing an active measure to prevent the series repeating over adjacent signal frames, the active measure being at least one of:changingthe pseudo-random symbol sequence;changingthe pseudo-random symbol sequence at a frame boundary;16 changing a modulation symbol at a frame boundary,wherein repetition of the series would otherwise occur but for the active measure.

17. A method according to claim 16, wherein pseudo-random symbol sequence change is implemented by at least one of:initializing a new pseudo-random symbol sequence with a different initializing parameter than one previously used; andinitializing a new pseudo-random symbol sequence with an initializing parameter which is shifted or scrambled relative to one previously used.

18. A method according to claim 16, wherein modulation symbol change is implemented by at least one of:using a modulation symbol which is different from that previously used; andusing a modulation symbol which is phase shifted relative to that previously used.

19. A method according to any of claims 16-18, wherein change is implemented by Radio Resource Control, RRC, between a network and UE.

20. A method as claimed in claim 19, wherein the implemented change is to a PRS sequence ID.

21. A computer program or a computer readable medium comprising instructions which, whenexecuted by an apparatus, cause the apparatus to perform at least the method of claims 13 to 20.w

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