Identification of active and passive entities in a wireless communication system using maximal length sequences

Abstract

The present disclosure proposes various entities in a wireless communication system, in particular, transmitter entities, digitally controllable scattering (DCS) entities, a receiver entity, and optionally a control entity. The receiver entity may identify, whether and which of the transmitter entities and DCS entities contributed, by respectively transmitting or scattering a signal, to form a receive signal received at the receiver entity. The receive signal may be received over one or more direct and / or indirect links, which the receiver entity may also identify. The identification by the receiver entity is possible due to the use of maximal length sequence identities (m-identities) determining maximal length sequences (m-sequences), wherein unique m-identities are used at the transmitter entities for transmitting signals and at the DCS entities for scattering impinging signals, and wherein unique m-identities are attributed to each direct link and indirect link.

Description

[0001]IDENTIFICATION OF ACTIVE AND PASSIVE ENTITIES IN A WIRELESS COMMUNICATION SYSTEM USING MAXIMAL LENGTH SEQUENCES TECHNICAL FIELD The present disclosure relates to wireless communications in a wireless communication system. The disclosure provides a transmitter entity, a digitally controllable scattering (DCS) entity, and a receiver entity, for the wireless communication system. A DCS may be also referred to as a reconfigurable intelligent surface (RIS), an intelligent reflecting surface (IRS), a large intelligent surface (LIS), or a smart repeater. The present disclosure also provides the wireless communication system. The wirelesscommunication systems can include more than one transmitter entity, DCS entity, and / orreceiver entity. The receiver entity can identify, whether and which of one or more transmitterentities and the one or more DCS entities contributed to a receive signal, which is received atthe receiver entity. The receiver entity can also identify, over which direct links and / or indirectlinks the respective signals contributing to the receive signal propagated to the receiver entity.The identification is enabled by the use of unique maximum length sequence identities (m-identities) at the transmitter entities, the DCS entities, and the receiver entity, respectively. BACKGROUND Conventional synchronization techniques using primary synchronization signals (PSS) or secondary synchronization signals (SSS), for example, in a 4thgeneration (4G) or fifth generation (5G) wireless communication system, consider the identification of direct links between transmitter entities and receiver entities, respectively. However, these conventional synchronization techniques do not consider the identification of indirect links, e.g., links including scattering at one or more DCS entities, which may contribute to a receive signal at the receiver entity. In other words, only the contributions of the transmitter entities to the receive signal can be identified by the receiver entity, while contributions of the DCS entitiescannot be identified by the receiver entity. SUMMARY The present disclosure and its solutions are based further on the following considerations.An exemplary conventional synchronization technique in a 4G or 5G system uses m-sequences,which are maximum length pseudo-random cyclic binary sequences. Therein, an m-sequenceis a cyclic shift of another m-sequence of a same generator polynomial. Thus, the ^^^sample of an m-sequence with ^^m-identity and length ^^is a modular cyclic shifted version of the original m-sequence, which may be written as follows: ^^(^ − ^^)^^^In other words, ^^(^ − ^^)^^^ means that each sample ^ of the m-sequence ^(^) iscyclically shifted by ^^. In a conventional direct link identification approach, the activelytransmitting entities (e.g., base stations) are assigned m-sequence identities, and the generatedm-sequence is modulated using Fourier transformation based multi-carrier techniques. Twoexamples of such Fourier based modulation techniques are the OFDM waveform and the CP- OFDM waveform:(1) For the orthogonal frequency-division multiplexing (OFDM) waveform, the ^^^transmitting entity constructs the OFDM symbol by mapping the m-sequence into the ^^length inverse discrete Fourier transform (IDFT) input, and as a result the ^^^sample of the signal after IDFT is given by: wherein ^ = √−1 is the pure imaginary number.(2) For a cyclic prefix (CP) OFDM (CP-OFDM) waveform, the ^^^ transmitting entityconstructs the CP-OFDM symbol by mapping the m-sequence into the ^^length IDFT input, and as a result the ^^^ sample of the signal after IDFT and CP extension is givenby: It should be noted that the m-sequence identity moves from residing within the cyclic shift before the Fourier transformation into residing within the phasor after Fourier transformation.In other words, the IDFT of an m-sequence ^ with cyclic shift ^^ could be re-written asfollows: ^^^^^^ ^(^) = ^(^) ^^ ^^wherein ^(^) denotes the IDFT of the original m-sequence ^(^) without cyclic shift. In otherwords, the IDFT of the m-sequence given by ^^(^ − ^ is equal to the multiplication of^^^^^^^the Inverse Fourier transform of ^(^), given by ^(^), times the phasor ^^^. This means that the cyclic shifting in the frequency domain is equivalent to a phasormultiplication in the time domain. In a conventional procedure, the receiver entity exploits them-sequence Kronecker like auto-correlation property, in order to identify the identities of thetransmitter entities. However, the conventional procedures do not guarantee identifyingbackscattered links (i.e., indirect links), if any, that contribute to the propagation of the signalfrom the transmitter entity to the receiver entity. Consequently, the conventional use of m-sequences does not allow for backscattered links identification. Moreover, when a signal travelsfrom a transmitter entity to a receiver entity after being scattered by multiple DCSs, the signalexperiences multiple DCS bounces. In conventional approaches, the multiple DCS bouncescase cannot be identified. In view of the above, an objective of this disclosure is to provide the receiver entity with thecapability to identify whether zero or one or more transmitter entities and / or whether zero oneor more DCS entities have contributed to a receive signal at the receiver entity. Anotherobjective is to identify different direct links and / or indirect links from a receive signal at thereceiver entity, that is, links over which one or more signals transmitted by at least one transmitter entity traversed before reaching the receiver entity. Another objective is to use the knowledge about the above identification in post-processing at the receiver entity, for example, to obtain a timing advance and signal to interference and / or noise ratio (SINR) of any identified direct or indirect link, and / or to perform a localization of the receiver entity. A purpose of this disclosure is thus to design the communications and DCS entities in a way that guarantees the above-mentioned identification capabilities. These and other objectives are achieved by the solutions in this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims. A first aspect of this disclosure provides a wireless communication system comprising one or more transmitter entities, one or more receiver entities, and one or more DCS entities, wherein: each transmitter entity is provided with a respective first m-identity of a first set of m-identities; each DCS entity is provided with a respective second m-identity of a second set of m-identities; each receiver entity is provided with one or more m-identities of a fourth set of m-identities, the fourth set of m-identities comprising one or more of the first m-identities and / or one or more of the second m-identities and / or one or more third m-identities of a third set of m-identities, wherein each indirect link from one of the one or more transmitter entities via at least one of the one or more DCS entities to the receiver entity is associated with one third m-identity of thethird set of m-identities; each transmitter entity is configured to generate a signal based on arespective unique maximal length sequence, m-sequence, determined by the respective first m-identity of the transmitter entity; each DCS entity is configured to scatter a signal impingingonto the DCS entity based on the respective second m-identity of the DCS entity, wherein thescattered signal is based on the respective second m-identity; and each receiver entity isconfigured to: obtain a receive signal; process the receive signal based on one or more uniquem-sequences, each of the one or more m-sequences being determined respectively by one ofthe one or more m-identities of the fourth set of m-identities; and identify, as a result of theprocessing, whether zero or one or more of the one or more m-sequences are comprised in the receive signal. The various sets of m-identities, which are used respectively at the one or more transmitter entities to transmit signals, at the one or more DCS entities to scatter impinging signals, and at the receiver entity to perform the identification(s), allow determining whether at least a part of the receive signal originated from one or more transmitter entities and / or whether at least a part of the receive signal was scattered by one or more DCS entities. Thus, the receiver entity can identify direct links and indirect links from the receive signal at the receiver entity, for instance, can identify a link that a signal transmitted by at least one transmitter entity traversed before reaching the receiver entity. In an implementation form of the first aspect, the wireless communication system further comprises: a control entity configured to determine at least one of the first set of m-identities, the second set of m-identities, the third set of m-identities, and the fourth set of m-identities. In an implementation form of the first aspect, the control entity is further configured to: provide at least one first m-identity of the first set of m-identities to respectively at least one transmitter entity; and / or provide at least one second m-identity of the second set of m-identitiesrespectively to at least one DCS entity; and / or provide at least one m-identity of the fourth setof m-identities to a receiver entity.Thus, the control entity is able to support the wireless communication system, particularly thereceiver entity, in obtaining the above-described advantages. In an implementation form, thecontrol entity may further be configured to construct all of the various sets of m-identities described above. In an implementation form of the first aspect, each first m-identity is associated with a respective transmitter entity and is thus indicative, at a receiver entity, of a direct link from the transmitter entity to the receiver entity. Thus, the receiver entity may identify transmitter entities and / or direct links from the receive signal based on the first set of m-identities. In an implementation form of the first aspect, the third set of m-identities comprises one ormore subsets of third m-identities; and a third m-identity of a respective subset is associatedwith an indirect link from one of the one or more transmitter entities via a respective number of the one or more DCS entities to the receiver entity, the respective number being one or larger and different for the subsets.Thus, the receiver entity may also identify indirect links from the receive signal based on thethird set of m-identities. The receiver entity may also determine a number of DCS bouncesrelated to an indirect link. It may also be possible for the receiver entity to determine theparticular DCS entities, by which at least a part of the receive signal was scattered, before reaching the receiver entity, based on the second set of m-identities. In an implementation form of the first aspect, if a signal impinging onto the DCS entity is based on a respective first m-identity of one of the one or more transmitter entities, the scattered signal is based on the respective first m-identity and on the respective second m-identity of the DCS entity.In an implementation form of the first aspect, if a signal impinging onto the DCS entity is basedon one or more respective second m-identities of one or more other DCS entities, the scattered signal is based on the one or more respective second m-identities of the one or more other DCS entities and on the respective second m-identity of the DCS entity.In an implementation form of the first aspect, each DCS entity comprises: a plurality ofscattering elements, each scattering element having a controllable phase shift; and a DCScontroller configured to control the scattering of the signal impinging onto the DCS entity by determining a respective phase shift configuration for the plurality of scattering elements based on the respective second m-identity of the DCS entity. As an example, the DCS entity may scatter one or more transmission signals from one or more transmitter entities, respectively, after the one or more transmission signals have been respectively scattered by either zero, one or more DCS entities in the wireless communication system. In an implementation form of the first aspect, the respective phase shift configuration determined for each DCS entity comprises a first phase shift configuration part and a secondphase shift configuration part; wherein the first phase shift configuration is a function of therespective second m-identity of the DCS entity, and the second phase shift configuration part is independent of the respective second m-identity. The DCS entity is configured to set the first phase shift configuration part based on the m- identity, which may lead to the scattering of the impinging signal based on the m-identity.In an implementation form of the first aspect, each receiver entity is further configured todetermine, based on the zero or one or more identified m-sequences comprised in the receivesignal at least one of: zero or one or more of the transmitter entities from which at least a partof the receive signal originated; zero or one or more of the DCS entities by which at least a partof the receive signal was scattered; zero or one or more indirect links over which at least a partof the receive signal arrived at the receiver entity; and / or zero or one or more direct links overwhich at least a part of the receive signal arrived at the receiver entity. In an implementation form of the first aspect, each receiver entity is further configured to:correlate the receive signal with each of a plurality of correlating signals, wherein each of thecorrelating signals is based on one of the one or more unique m-sequences that are determinedby the m-identities of the fourth set of m-identities.The above-described is an example of how the receiver entity can efficiently identify zero orone or more m-sequences in the receive signal.In an implementation form of the first aspect, the receiver entity is configured to determine thezero or one or more transmitter entities, and / or the zero or one or more DCS entities, and / or the zero or one or more indirect links, and / or the zero or one or more direct links, based on the result of the correlating with the plurality of correlating signals. In an implementation form of the first aspect, each receiver entity is further configured toperform a post-processing process comprising: determining a timing advance for each of oneor more direct links and / or for each of one or more indirect links; and / or estimating a SINR forthe one or more direct links and / or the one or more indirect links. The receiver entity may obtain the timing advance and also the SINR of each identified link, and may perform a localization procedure based thereon. The receiver entity may obtain an estimate of interfering signals scattered from different DCSs (after one or multiple bounces) or received via direct link.A second aspect of this disclosure provides a method for a wireless communication systemcomprising one or more transmitter entities, one or more receiver entities, and one or more DCSentities, the method comprising: providing each transmitter entity with a respective first m-identity of a first set of m-identities; providing each DCS entity with a respective second m-identity of a second set of m-identities; providing each receiver entity with one or more m-identities of a fourth set of m-identities, the fourth set of m-identities comprising one or more of the first m-identities and / or one or more of the second m-identities and / or one or more thirdm-identities of a third set of m-identities, wherein each indirect link from one of the one ormore transmitter entities via at least one of the one or more DCS entities to the receiver entityis associated with one third m-identity of the third set of m-identities; generating, by atransmitter entity, a signal based on a respective unique maximal length sequence, m-sequence,determined by the respective first m-identity of the transmitter entity; scattering, by a DCSentity, a signal impinging onto the DCS entity based on the respective second m-identity of the DCS entity, wherein the scattered signal is based on the respective second m-identity of theDCS entity; obtaining, by a receiver entity, a receive signal; processing, by the receiver entity,the receive signal based on one or more unique m-sequences, each of the one or more m- sequence being determined respectively by one of the one or more m-identities of the fourth setof m-identities; and identifying, by the receiver entity as a result of the processing, whether zeroor one or more of the one or more m-sequences are comprised in the receive signal. The method of the second aspect may have implementation forms, which correspond to the above-described implementation forms of the wireless communication system. The method of the second aspect and its implementation forms achieve the same advantages as described above for the wireless communication system of the first aspect and its respective implementation forms. A third aspect of this disclosure provides a computer program comprising instructions which, when the program is executed by a computer of the transmitter entity, the DCS entity, or the receiver entity, respectively, cause the computer to perform the steps of the transmitter entity,or the DCS entity, or the receiver entity of the method according the second aspect.A fourth aspect of this disclosure provides a non-transitory storage medium storing executableprogram code which, when executed by a processor, causes the method according to the secondaspect or any of its implementation forms to be performed.A fifth aspect of this disclosure provides a transmitter entity for a wireless communicationsystem, wherein the transmitter entity is provided with a first m-identity of a first set of m-identities, and wherein the transmitter entity is configured to generate a signal based on a unique m-sequence determined by the first m-identity of the transmitter entity. The transmitter entity may be provided with a different m-identity from the first set of m-identities than other transmitter entities in the wireless communication system. Thus, a receiverentity can distinguish the transmission signal of the transmitter entity from transmission signals of other transmitter entities.A sixth aspect of this disclosure provides a DCS entity for a wireless communication system,wherein the DCS entity is provided with a second m-identity of a second set of m-identities, and wherein the DCS entity is configured to scatter a signal impinging onto the DCS entity based on the second m-identity of the DCS entity, wherein the scattered signal is based on the second m-identity. The DCS entity may be provided with a different m-identity than other DCS entities in the wireless communication system. Thus, a receiver entity can distinguish the signals scattered bydifferent DCS entities. Thus, a receiver entity may identify, whether at least a part of a receivesignal at the receiver entity is a scattered signal that stems from the DCS entity. In an implementation form of the sixth aspect, if a signal impinging onto the DCS entity isbased on a respective first m-identity of one of one or more transmitter entities in the wirelesscommunication system, the scattered signal is based on the respective first m-identity and onthe second m-identity of the DCS entity. In an implementation form of the sixth aspect, if a signal impinging onto the DCS entity isbased on one or more respective second m-identities of one or more other DCS entities in thewireless communication system, the scattered signal is based on the one or more respective second m-identities of the one or more other DCS entities and on the respective second m- identity of the DCS entity. In an implementation form of the sixth aspect, the DCS entity comprises: a plurality of scattering elements, each scattering element having a controllable phase shift; and a DCS controller configured to control the scattering of the signal impinging onto the DCS entity by determining a phase shift configuration for the plurality of scattering elements based on the second m-identity of the DCS entity. In an implementation form of the sixth aspect, the phase shift configuration determined for theDCS entity comprises a first phase shift configuration part and a second phase shiftconfiguration part; wherein the first phase shift configuration is a function of the respective second m-identity of the DCS entity, and the second phase shift configuration part is independent of the second m-identity. A seventh aspect of this disclosure provides a receiver entity for a wireless communication system, wherein the receiver entity is provided with one or more m-identities of a fourth set of m-identities, the fourth set of m-identities comprising one or more of the first m-identities (asmentioned above for the transmitter entity of the fifth aspect) and / or one or more of the secondm-identities (as mentioned above for the DCS entity of the sixth aspect) and / or one or morethird m-identities of a third set of m-identities, wherein each indirect link from one of one ormore transmitter entities via at least one of one or more DCS entities to the receiver entity isassociated with one third m-identity of the third set of m-identities, wherein the receiver entity is configured to obtain a receive signal; process the receive signal based on one or more unique m-sequences, each of the one or more m-sequences being determined respectively by one ofthe one or more m-identities of the fourth set of m-identities; and identify, as a result of theprocessing, whether zero or one or more of the one or more m-sequences are comprised in the receive signal. Thus, the receiver entity is provided with the knowledge of the m-identities in these various sets, and may thus use them to identify transmitter entities and / or DCS entities when receivingone or more receive signals. The receiver entity may identify, in a receive signal, different directlinks and indirect links, which one or more transmission signals transmitted by the one or more transmitter entities followed, before reaching the receiver entity. The receiver entity may also identify, from the receive signal, which of zero or one or more transmitter entities sent atransmission signal, and by which of zero or one or more DCS entities the transmission signalwas scattered before reaching the receiver entity.In an implementation form of the seventh aspect, each first m-identity is associated with arespective transmitter entity and is thus indicative, at the receiver entity, of a direct link from the transmitter entity to the receiver entity.In an implementation form of the seventh aspect, the third set of m-identities comprises one ormore subsets of third m-identities; and a third m-identity of a respective subset is associatedwith an indirect link from one of the one or more transmitter entities via a respective number of the one or more DCS entities to the receiver entity, the respective number being one or larger and different for the subsets. An eighth aspect of this disclosure provides a control entity for a wireless communication system, wherein the control entity is configured to determine at least one of the first set of m- identities, the second set of m-identities, the third set of m-identities, and the fourth set of m- identities. In an implementation form of the eighth aspect, the control entity is further configured to: provide at least one first m-identity of the first set of m-identities to respectively at least onetransmitter entity in the wireless communication system; and / or provide at least one second m-identity of the second set of m-identities respectively to at least one DCS entity in the wirelesscommunication system; and / or provide at least one m-identity of the fourth set of m-identitiesto a receiver entity in the wireless communication system.In an implementation form of the eighth aspect, the receiver entity is further configured to determine, based on the zero or one or more identified m-sequences comprised in the receive signal at least one of: zero or one or more of the transmitter entities from which at least a part of the receive signal originated; zero or one or more of the DCS entities by which at least a part of the receive signal was scattered; zero or one or more indirect links over which at least a part of the receive signal arrived at the receiver entity; and / or zero or one or more direct links over which at least a part of the receive signal arrived at the receiver entity. In an implementation form of the eighth aspect, the receiver entity is further configured to:correlate the receive signal with each of a plurality of correlating signals, wherein each of thecorrelating signals is based on one of the one or more unique m-sequences that are determinedby the m-identities of the fourth set of m-identities. In an implementation form of the eighth aspect, the receiver entity is configured to determine the zero or one or more transmitter entities, and / or the zero or one or more DCS entities, and / or the zero or one or more indirect links, and / or the zero or one or more direct links, based on the result of the correlating with the plurality of correlating signals. In an implementation form of the eighth aspect, the receiver entity is further configured to perform a post-processing process comprising: determining a timing advance for each of one or more direct links and / or for each of one or more indirect links; and / or estimating a signal-to-interference-plus-noise ratio, SINR, for the one or more direct links and / or the one or moreindirect links. In summary of the above-mentioned aspects and implementation forms, the solutions of thisdisclosure provide a receiver entity of a wireless communication system with an identificationcapability of direct links and indirect links (backscattered by zero or one or more DCS entities)that, for instance, a transmission signal of a transmitter entity undergoes, before reaching thereceiver entity. The solutions of this disclosure are based on designing and distributing uniquem-identities among the one or more transmitter entities, the one or more DCS entities, and theone or more receiver entities, in order to guarantee a unique m-identity for each transmitter entity and DCS entity and / or for each considered indirect link. This identification capability atthe receiver entity may be exploited, in order to achieve different objectives and applications,such as measurements related to different received paths (e.g., timing advance, SINR),interference mitigation and localization.The solution of this disclosure, which uses the m-identity distribution for signal transmission atthe transmitter entities and DCS scattering at the DCS entities, also allows identifying contributions of indirect links for the case where the indirect links result from more than one DCS entity (scattering) bounce. The solutions of this disclosure are applicable to a scenario with multiple transmitter entities and multiple DCS entities in the propagation environment and / or the wireless communication system, wherein a transmission signal may reach the receiver entity after passing through different direct and indirect links. A direct link may be defined as the trajectories the transmission signal emitted from a transmitter entity undergoes to reach the end-user without being reflected by any DCS entity. An indirect or backscattered link may be defined as the trajectory or trajectories the transmission signal emitted from a transmitter entity undergoes to reach the receiver entity after being bounced (scattered) by one or more DCS entities. A DCS entity may contain scattering elements, each having a controllable phase shift. Sincethe scattering elements do not have to be connected to RF chains, the DCS entity may beconsidered as a passive node, but is not limited thereto in this disclosure. This in contrast to atransmitter entity, which may have active RF chains, and hence is considered as active node inthis disclosure. It has to be noted that all entities, elements, units and means described in the present application could be implemented by software or hardware elements or any kind of combination thereof. All steps performed by the various entities described in the present application, as well as the functionalities described to be performed by the various entities, are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity, which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented by respective software or hardware elements, or any kind of combination thereof. BRIEF DESCRIPTION OF DRAWINGS The above described aspects and implementation forms are explained in the following description in relation to the enclosed drawings, in which:FIG. 1 shows a wireless communication system including a transmitter entity, a DCSentity, and a receiver entity according to this disclosure.FIG. 2 shows an exemplary allocation of m-identities in a wireless communicationsystem according to this disclosure by a control entity.FIG. 3 illustrates links between transmitter entities, DCS entities, and receiver entitiesin a wireless communication system according to this disclosure.FIG. 4 shows an example of a wireless communication system according to thisdisclosure.FIG. 5 shows a flow-diagram of a method according to this disclosure.FIG. 6 shows exemplary configurations of DCS scattering surfaces.DETAILED DESCRIPTION OF EMBODIMENTS FIG.1 shows a wireless communication system 100 according to this disclosure. As illustrated, the wireless communication system 100 comprises at least one transmitter entity 110, at leastone DCS entity 130, and at least one receiver entity 120. Notably, the wireless communicationsystem 100 can comprise multiple transmitter entities 110, multiple DCS entities 130, andmultiple receiver entities 120. The wireless communication system 100 may be a wirelessnetwork, for example, a cellular network like a 4G or 5G network or WiFi network or AdHoc network. The one or more transmitter entities 110 may be network devices like communication nodes or base stations (BSs) or the like, and the one or more receiver entities 120 may be communication nodes or end-user devices like mobile phones, terminal devices, or other user equipment (UE).As shown in FIG. 1, the at least one transmitter entity 110 is provided with a first m-identity111 of a first set of m-identities. Each transmitter entity 110 in the wireless communicationsystem 100 may be provided with a respective (different) first m-identity 111 of the first set ofm-identities. Each transmitter entity 110 is configured to generate a respective signal 112 based on a respective unique m-sequence determined by the respective first m-identity 111 of said transmitter entity 110.As further shown in FIG. 1, the at least one DCS entity 130 is provided with a second m-identity131 of a second set of m-identities. Each DCS entity 130 in the wireless communication system100 may be provided with a respective (different) second m-identity 131 of the second set ofm-identities. Each DCS entity 130 is configured to scatter a respective signal 132 impinging onto the DCS entity 130 based on the respective second m-identity 131 of said DCS entity 130.The respective scattered signal 133 is then based on the respective second m-identity 131 ofsaid DCS entity 130. The impinging signal 132 may be any kind of signal. However, theimpinging signal 132 may be, or may comprise, the transmission signal 112 of the transmitterentity 110. The impinging signal 132 could also arrive from another DCS entity 130 in thewireless communications system 100, i.e., may be or may comprise the scattered signal 133produced by scattering the impinging signal 132.As further shown in FIG. 1, the at least one receiver entity 120 is provided with one or more m-identities 111, 121, 131 of a fourth set of m-identities. Each receiver entity 120 may be providedwith the one or more m-identities 111, 121, 131 of the fourth set. The fourth set of m-identitiescomprises one or more of the first m-identities 111 and / or one or more of the second m-identities 131 and / or one or more third m-identities 121 of a third set of m-identities. The third m-identities 121 are associated with indirect links 140 each between a transmitter entity 110 and a receiver entity 120 in the wireless communication system 100. Each indirect link 140 is particularly from one of the one or more transmitter entities 110 via at least one of the one ormore DCS entities 130 to a receiver entity 120, and is associated with one of the third m-identities 121 of the third set. Each receiver entity 120 is configured to obtain a receive signal122, and is configured to process the receive signal 122 based on one or more unique m-sequences. Thereby, each of these one or more m-sequences is determined respectively by oneof the one or more m-identities 111, 121, 131 of the fourth set of m-identities. Each receiverentity 120 is further configured to identify, as a result of the processing, whether zero or one ormore of the one or more m-sequences, which correlated to the one or more m-identities 111,121, 131 of the fourth set, are comprised in the receive signal 122. Accordingly, the receive signal 122 may include one or more transmission signals 112respectively originating from one or more transmitter entities 110, and respectively scatteredby zero or one or more DCS entities 130 of the wireless communication system 100. Forexample, the transmission signal 112 shown in FIG. 1 of the at least one transmitter entity 110could be scattered, as the impinging signal 132, by the at least one DCS entity 130, and the scattered signal 133 may then be received by the receiver entity 120 as the receive signal 122.As another example, the transmission signal 112 could be received by the receiver entity 120as the receive signal 122 directly after propagation through the wireless channel over a directlink 150, without scattering at any DCS entity 130. In either case, the receiver entity 120 isconfigured to process the receive signal 122 as described above.A specific example, where the receiver entity 120 of FIG.1 identifies a transmission signal 112of the transmitter entity 110 of FIG. 1, is as follows. The transmitter entity 110 generates thetransmission signal 112 based on the first m-identity 111, wherein particularly the transmission signal 112 is based on a unique m-sequence determined by the first m-identity 111. The DCSentity 130 scatters an impinging signal 132, which includes the transmission signal 112generated by the transmitter entity 110, based on the second m-identity 131. The scattered signal 133 thus includes a signal containing a unique m-sequence that is based on the first m-identity111 and the second m-identity 131. The receiver entity 120 receives this scattered signal 133 asa part of the receive signal 122. The scattered signal 133 is associated with an m-identity 121from the third set of m-identities, as it is received over an indirect link 140. Notably, thereceiver entity may also receive, as another part of the receive signal 122, the transmissionsignal 112 generated by the transmitter entity 110 directly over a direct link 150 (without DCSscattering). The receiver entity 120 can then process the receive signal 122 based on the one ormore of unique m-sequences determined by the fourth set of m-identities, and can determinethat the m-sequences based on the first m-identity 111 and based on the second m-identity 131and based on the third m-identity 121 are included in the receive signal 122. In this way, the receiver entity 120 can identify the transmitter entity 110 that is involved in the signaltransmission, and can also identify the DCS entity 130 that is involved in signal scattering. Thereceiver entity 120 may also identify the direct link 150 and indirect link(s) 140, over which thetransmission signal 112 arrives at the receiver entity 120. The indirect link(s) 140 may involve one, or more DCS bounces. The entities 110, 120, 130 may respectively comprise a processor or processing circuitry (not shown) configured to perform, conduct or initiate the various operations of the respective entity 110, 120, 130 described herein. The processing circuitry may comprise hardware and / or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field- programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The entities 110, 120, 130 may respectively further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor or by the processing circuitry, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor or the processing circuitry, causes the various operations of the respective entity 110, 120, 130 to be performed. In one embodiment, the processing circuitry comprises one or more processors and a non-transitory memory connected to the one or more processors. The non- transitory memory may carry executable program code which, when executed by the one or more processors, causes the respective entity 110, 120, 130 to perform, conduct or initiate the operations or methods described herein. As shown in FIG. 2, the wireless communication system 100 may further comprise a controlentity 200 (here exemplarily referred to as “M-Seq Allocator”, since it may optionally be ableto allocate m-identities associated with m-sequences). The control entity 200 may be configuredto determine at least one of the first set of m-identities, the second set of m-identities, the thirdset of m-identities, and the fourth set of m-identities. For instance, the control entity 200 maybe configured to design and / or to construct at least one of the first, second, third, and fourth setof m-identities. Notably, each m-identity in any set of m-identities is configured to determine aunique m-sequence.The first m-identities 111 of the first set may be obtained and / or designed by the control entity200 for being individually provided to the one or more transmitter entities 110 in the wirelesscommunication system 100. The second m-identities 131 of the second set may be obtainedand / or designed by the control entity 200 for being individually provided to one or more DCSentities 130 in the wireless communication system 100. For example, the control entity 200may be configured to provide a signalling to the transmitter entity 110 in FIG. 2 (“ithTransmitter”), in order to signal one first m-identity 111 from the first set to the transmitterentity 110. Generally, the control entity 200 may signal a different first m-identity 111 from thefirst set to each of the one or more transmitter entities 110 in the wireless communication system100. As another example, the control entity 200 may be configured to provide a signalling tothe DCS entity 130 in FIG. 2 (“jth DCS”), in order to signal one second m-identity 131 from thesecond set to the DCS entity 130. Generally, the control entity 200 may signal a different second m-identity 131 from the second set to each of the one or more DCS entities 130 in the wireless communication system 100. However, the transmitter entities 110 and DCS entities 130 could also obtain the respective m-identities 111, 131 in a different manner, for instance, byconfiguration. As another example, the control entity 200 may be configured to provide a signalling to the receiver entity 120 in FIG.2 (“Receiver”), in order to signal the one or more m-identities 111, 121, 131 from the fourth set of m-identities to the receiver entity 120.Generally, the control entity 200 may signal the one or more m-identities 111, 121, 131 of thefourth set to one or more receiver entities 120 in the wireless communication system 100. The present disclosure thus proposes designing and allocating m-identities 111, 121, 131 among the transmitter entities 110 and DCS entities 130 of the wireless communication system 100, such that when an m-sequence based transmission signal 112 propagates to a receiver entity 120 via a backscattered (i.e., indirect) link 140, it experiences a unique overall frequency shift based on the second m-identities 131 that are allocated to the DCSs 130 that correspond to and / or define the backscattered link 140. The proposed m-identity allocation and related signal transmission and DCS frequency shifting may guarantee a different unique frequency shift for each of the considered direct and indirect links 140. Hence, signals arriving to the receiver entity 120 via different links experience a different frequency shift. Consequently, the signals arriving to the receiver entity 120 via different links and observed, for example, after DFT processing, correspond each to a unique m-sequence with its unique m-identity, thus enabling the capability of identifying the different direct links 150 and indirect links 140. This identification capability could be exploited by the receiver entity 120 for different objectives such as measurements related to different received paths (e.g., timing advance, SINR) and localization. FIG. 2 visualizes the following steps, which may be implemented in the wireless communication system 100. A first step relates to the control entity 200. The control entity 200 can design and allocate the m-identity sets including the m-identities 111, 121, 131, and optionally some parameters. In the first step, the following may be determined jointly by the control entity 200.^ ^^: The length of the m-sequence.^ Ω^^ : The first set of ^^^ first m-identities 111 that could be allocated to the transmitterentities 110.^ Ω^^^: The second set of ^^^^ second m-identities 131 that could be allocated to the DCSentities 130.^ Ω^ : The third set of ^^ third m-identities 121 that could be allocated to the overallbackscattered (indirect) links 140.^ Ω^,^: A subset of ^^,^ third m-identities 121 of the third set that could be allocated to thebackscattered (indirect) links 140 with ^ DCS bounces. That is the third set of m-identitiesmay comprise one or more subsets of third m-identities 121, wherein a third m-identity 121 of a respective subset is associated with an indirect link 140 from one of the one or more transmitter entities 110 via a respective number ^ of the one or more DCS entities130 to the receiver entity 120. The number ^ is one or larger and different for the subsets.Therein, the following holds (Eq.1).In equation 1, ^ denotes the maximum number of DCS bounces that a backscattered link 140can support, while still being uniquely identifiable. The choice of ^ is usually related to a linkbudget constraint. A second step relates to the transmitter entity 110, which generates an m-sequence based on its first m-identity 111 (e.g., cyclic shift), and emits the corresponding inverse Fourier transform based symbol(s) as the transmission signal 112. A third step relates to the DCS entity 130 and the design of the DCS phase configuration vector^(^) – for the scattering elements of the DCS entity 130 – wherein: This vector corresponds to a phase shift configuration, which comprises two phase shift configuration parts. The first phase shift configuration part is called a DCS common phasor, and the second phase shift configuration part is called a DCS element-specific phasor. The first phase shift configuration is a function of the respective second m-identity 131 of the DCS entity 130, and the second phase shift configuration part is independent of the respective second m- identity 131. In particular:^ The DCS common phasor ^^^^(^) ∈ ℂ^×^^ is designed based on the allocated second m-identity 131, so that the scattered signal corresponds to a frequency shifted version of the impinging signal 132 and the frequency shift is based on the allocated m-identity.^ The DCS element-specific phasor is an available degree of freedom thatcould be exploited to achieve different objectives where ^ denotes the number ofscattering elements of the DCS entity 130.A fourth step relates to the receiver entity 120, e.g., the end-user device. The receiver entity 120 may utilize pre-generated correlating signals that correspond to all m-sequences withinΩ^^ ∪ Ω^ in order to identify the existing direct and backscattered links 140. The detected peakscould go through one or more different post-processing procedures depending on the desired objective such as measurements (e.g., timing advance, SINR), interference mitigation and localization. The proposed approach solves the problem of identifying, for each of a plurality of links perceived by any of the plurality of receiver entities 120, all the active transmitter entities 110and passive DCS entities 130 that create the paths that define a link. A link can be representedby a sequence of its active contributor or active and passive contributors. Several representations can be present in a link that would correspond to different orders of the sequences of its active contributor or active and passive contributors. The proposed solution of this disclosure includes a joint design of transmitted signal 112 and DCS common phasor based on m-sequences, wherein:^ The transmission signal 112 sent by each transmitter entity 110 is based on inverseFourier transformation of an m-sequence.^ The DCS common phasor for each DCS entity 130 is configured based on a second m-identity 131, so that the scattered signal 133 corresponds to a frequency shifted version of the impinging signal 132, and the frequency shift is based on the allocated second m- identity 131.^ At the receiver entity 120, the received signal 122 is processed to extract the m-identities111, 121, 131 of the transmitter entities 110, and / or DCS entities 130, and / or direct links150 and / or indirect links 140, for instance, in order to detect existing direct 150 andbackscattered 140 links as well as interfering contributions. This may be done byconsidering the m-sequence of the transmitted signal 112 and the different m-sequences and related frequency shift applied by each DCS entity 130.^ The identified links could be optionally further post-processed for different applications(e.g., timing advance estimation etc.).^ The constructed m-sequences are designed such that each of the considered direct 150and backscattered 140 links have unique m-identities.^ The m-sequences may be designed by a control entity 200 (which may be a physical orlogical entity, and / or which may be a localized or distributed entity).^ The construction of the m-sequences can be obtained through prior information fixed orlearned. The process of sequence construction can also be dynamic.An example of a wireless communication system 100, in which different direct links 150 andindirect links 140 are formed between transmitter entities 110 (“TX”, e.g., BSs) and receiver entities 120 (“RX”, e.g., mobile or terminal devices) via zero or one or more DCS entities 130, is shown in FIG.3.As can also be seen in FIG. 3, each DCS entity 130 comprises a plurality of scattering elements,wherein each scattering element has a controllable phase shift. Each DCS entity 130 may comprise a DCS controller, which is configured to control the scattering of the respectively impinging signal 132 onto the DCS entity 130, by setting a phase shift configuration for the plurality of scattering elements based on the second m-identity 131 configured at the respective DCS entity 130. The DCS controller may in this case be configured to set the first phase shift configuration part as a function of the second m-identity 131 configured at the respective DCS entity 130, and to set the second phase shift configuration part independent of that m-identity.The scattering elements may be arranged as or may form a scattering surface of the DCS entity130. FIG. 6 shows in this respect exemplary configurations of DCS scattering surfaces. Asdepicted in FIG. 6, the DCS entity 130 can be implemented as a single block or as multiple blocks, as plane surfaces or any type of surface, an aggregation of surfaces or a subsurface of one or more DCS entities.In the following, some more details and exemplary embodiments of the above described foursteps are described.In the first step, the aim is to design the m-identity sets Ω^^ , Ω^^^ and Ω^ that specify the m-identities that could be allocated to the transmitting entities 110 (and that are related to the directlinks 150, as each first m-identity 111 may be indicative of a direct link 150 at the receiverentity 120), DCS entities 130, and backscattered (indirect) links 140, respectively. Different possible embodiments are given below.The design and allocation procedure are based on different properties and conditions that areused jointly and that could be listed as follows.^ The length of the m-sequence is equal to the number of m-identities that are sharedbetween the direct links 150 and the backscattered links 140: Different ways could be used to determine these parameters(^^ , ^^^ , ^^). For example,based on the available m-sequence length and targeted number of transmitting entity identities, ^^ may be determined. Or, for example, based on the targeted number oftransmitting nodes identities and the required length of the m-sequence ^^may be determined.^ In order for the backscattered links 140 and the direct links 150 (i.e., the transmittingentities 110) to be uniquely identified, their corresponding m-identity sets should not have any common element. Thus, the design process of the m-identity sets should guarantee the two following conditions: ∩ ^ ^^^ Ω^,^ = {^^^^^ ^^^} (Eq. 5)^ The number of identifiable backscattered links 140 is related to the number of consideredDCS entities ^^^^ and the maximum number of supported DCS bounces ^ where ^ The DCS scattering process is equivalent to a multiplication process in time domainwhere the time domain incident signal (e.g. a signal that includes the m-sequence based signal) is multiplied by the DCS phase configuration vector ^(^) = .^ The time domain multiplication of an impinging m-sequence based signal by the designedfrequency shifting common phasor is equivalent to a cyclic shift in the frequency domain of the transmitted m-sequence. Thus, a transmitted m-sequence based signal obtained from Fourier based modulation of an m-sequence with identity ^^, and after being scattered by the DCS configured based on m-sequence identity ^^ (e.g. DCS^common phasor given by = ^^^^^^ ^ ^^), results in another m-sequence based signal that when converted to frequency domain at the receiver using Fourier transformation results in an m-sequence with identity ^^where ^^is the modular summation of the identity of the impinging m-sequence based signal and the identity of the m-sequence based DCS phase configuration vector thus ^^ = ^^^^^^ + ^^ , ^^^.A design example of the identity sets for the case where ^ = 1, is as follows:a. Design Ω^^ elements so that the ^^ modular distance ^ between any two adjacentelements is the same (e.g., for ^^=100, choose {1,11,21, … 91}, wherein ^ = 9).The modular distance ^ between two elements is defined as the number of elements thatlie between the two considered elements within the set.b. The number ^^^^ of identities to be allocated to the DCS entities is equal to the designedfixed modular distance between any two adjacent elements of the Ω^^set. (e.g., with then ^^^^ = ^ = 9).c. Design Ω^^^ so thatI. The Ω^^^ elements are continuous. This means the modular distance between anytwo adjacent elements of Ω^^^ is equal to zero ^ = 0.II. The first element in the Ω^^^ set is the same as the first element of the Ω^^ set (e.g.,for ^^ = 100 then Ω^^^ ∶ {1,2,3,4,5, … ,9}).III. The resulting backscattered links set Ω^ is the sets addition (known as Minkowskiaddition) of Ω^^and Ω^^^where resulting Ω^will satisfy condition in Eq. 4 (e.g.,for ^^ = 100 , Ω^^: {1,11,21, … ,91} and Ω^^^ ∶ {1,2,3,4,5, … ,9} thenΩ^: ^{2,3,4, … ,10} ∪ {12,13,14, … ,20} ∪ … ∪ {92,93,94, … ,100}^.In the second step, the transmitter entity 110 constructs an m-sequence using its allocated first m-identity ^^and modulates it into a baseband waveform using Fourier based modulation. Different multi-carrier modulation techniques can be used as long as they are based on the Fourier transformation. Examples of that are the OFDM and CP-OFDM waveforms as described above. The third step is about the configuration of the DCS phase configuration vector, which is written as a function of two independent phasors: a. The DCS common phasor ∈ ℂ^×^ may be configured in correspondence with theadopted transmitting technique of the transmitter entity 110, while using its assigned- sequence identity ∈ Ω^^^ . Below, different configurations examples are given thatcorrespond to the different transmitting techniques mentioned in the second step. I. OFDM incident waveform: The DCS common phasor is designed using itsallocated m-sequence identity ^^and length ^^ II. CP-OFDM incident waveform: The DCS common phasor is designed using itsallocated m-sequence identity ^^and length ^^ b. The DCS element specific phasor ^^^ ∈ ℂ^×^ could be designed to achieve differentobjectives where it is independent from DCS common phasor design process. A design example of the DCS element specific phasor ^^^is to be configured to maximize the received signal power at the receiver or to optimize certain quality metrics.In the fourths step, the objective of the receiver entity 120 is to identify the direct and non-directlinks 150, 140 that the transmitted m-sequence based signals undergo to reach the receiver entity 120, and which result from scattering / bouncing by none, one or multiple DCS entities 130. A signal arriving via a direct link 150 has the form: A signal arriving via a backscattered link 140 has the form: (^^ + ^^) ∈ Ω^ (Eq. 10)To do so, the receiver entity 120 uses its prior-knowledge of the m-identity sets to process the overall received signal 122. The receive signal 122 at the receiver entity 120 might contain different m-sequence based signals, coming from different transmitting entities 110 after none, one, or multiple bounces by the DCS entities 130. In a first case, an initial synchronization may exist between the receiver entity 120 andtransmitter entity 110 (e.g., coarse synchronization). The receive signal 122 could pass throughthree major processing stages: pre-processing, identification process, post-processing.An example of the pre-processing stage is transforming the time-domain receive signal 122 intothe frequency domain by means of (CP)-OFDM demodulations. In fact, the Fourier transformation of the received signal 122 recovers the m-sequence nature of any transmissionsignals 112 and scattered signals 133 in the receive signal 122.^ The Fourier transformation of a signal arriving via a direct link 150, as described in Eq.9 results in an m-sequence that has the same identity of the corresponding transmitter: ^ (Eq. 11) Where the Fourier transformation^ he time domain signal ^ ^ ^^^^^^^of t ( ) ^^ results in ( →) a cyclic shift of the Fouriertransformation of ^(^).^ The Fourier transformation of a signal arriving via a backscattered link 140, as describedin Eq. 10, results in an m-sequence with a new identity that belongs to the overallbackscattered links identities set Ω^. As the two equations Eq.11 and Eq.12 above show, due to the properties of the m-sequences and to our proposed m-sequence based transmitted signals 112 together with m-sequence identity based DCS frequency shifting, the FFT of a signal received via a direct or backscattered link 140 results in an m-sequence whose identity depends on the transmitted m-identity and thefrequency shift applied by the DCS entity 130. Since the received signal 122 includes thesuperposition of the signals arriving at the receiver entity 120 via the different direct links 150and backscattered links 140, due to FFT properties, the frequency domain signal after thepreprocessing stage includes the superposition of the corresponding m-sequences. An example of the identification stage is correlating the output of the preprocessing stage with different correlating sequences, m-sequences, in order to identify the existing direct andbackscattered links 150, 140. These correlating sequences are generated at the receiver entity120 using its prior knowledge of the m-sequence identity sets (i.e., the fourth set of m-identities).The output of the correlation process will result in a peak in power when the consideredcorrelating signal matches one of the received direct or backscattered link m-sequence identity.Regarding the post-processing stage, the output of the identification stage is post-processed toget different measurements / metrics. For example, the identified peaks could be used to estimateand / or refine the timing advance of the considered direct or non-direct link, and / or to estimatethe SINR of the considered direct or non-direct link.In a second case, no initial synchronization exists between receiver entity 120 and transmitterentity 110. The receiver entity 120 operates a sliding-window correlation in the time domain using FFT processing. The correlation in time domain can be implemented as follows.For each m-sequence ^(^) , the circular correlation of the received signal ^(^) with the^(^) over a sliding window of ^^ length, can be written as follows: In this equation ^(^) = [^(^), ^(^ + 1), … ^(^ + ^^)], ^(^) represents the ^-^ℎ sample of thereceived signal and ^ = ^^(0), ^(1), … , ^(^^), 0^,^ 0^ …^^ 0 ^ is the zero padded transmitted m-^^^^^sequence based signal. It should be noted that the vector ^ is zero padded in order to allow forthe fast implementation of the Fourier transformation, the FFT, where ^^a prime number andthe FFT length should be of the form 2^ with ^ being a positive integer. It should beemphasized that other implementations of the sliding-window correlation are possible.The correlation profile ^(^) ∈ ℂ^^×^ is post-processed to detect the list of candidate m-sequences included in the receive signal 122 as well their relative time advance.In order for the correlation process to function properly and for the receiver entity 120 togenerate the needed direct and backscattering links correlating signals, the receiver entity 120should be provided with prior information about the m-identity sets. Below, different examplesbased on different level of available information at the end user are provided.(1) Available information: {^^ , Ω^^ , Ω^}a. Based on this knowledge the receiver entity 120 can generate correctly the directand the backscattered links correlating signals. b. This allows the receiver entity 120 to possibly identify the existing direct andbackscattered links within its received signal 122.c. The receiver entity 120 will be capable of distinguishing between a detected directlink 150 and a detected backscattered link 140.d. The receiver entity 120 cannot distinguish the backscattered links that havedifferent number of DCS bounces.(2) Available information: {^^ , Ω^^ , Ω^^^, ^ }a. Same a, b, c of the previous example.b. The knowledge of the Ω^^^ set and ^ parameter gives the receiver entity 120 avisibility of how to construct the Ω^set. This knowledge allows the receiver entity 120 to distinguish between the backscattered paths that have different number of DCS bounces.FIG. 4 shows an exemplary embodiment of a wireless communication system 100 according tothis disclosure. A signaling example is provided, wherein the ^thtransmitter entity 110 and the^th DCS entity 130 are allocated the ^^ and ^^ m-identities, respectively. The m-identities areused by the transmitter entity 110 to construct its m-sequence and by the DCS entity 130 toapply its frequency shift. This happens in a synchronized manner, in order to result in an m-sequence at the receiver entity 120, after the DFT processing, with a new identity that thereceiver entity 120 could extract via correlation and later use it in different post processing.FIG. 5 shows a flow-diagram of a method 500 according to this disclosure. The method 500may be performed in a wireless communication system 100 comprising one or more transmitterentities 110, one or more receiver entities 120, and one or more DCS entities 130.The method 500 comprises a step 501 of providing each transmitter entity 110 with a respectivefirst m-identity 111 of a first set of m-identities. Further, a step 502 of providing each DCSentity 130 with a respective second m-identity 131 of a second set of m-identities. Further, a step 503 of providing each receiver entity 120 with one or more m-identities 111, 121, 131of a fourth set of m-identities. The fourth set of m-identities comprises one or more of the firstm-identities 111 and / or one or more of the second m-identities 131 and / or one or more third m- identities 121 of a third set of m-identities. Each indirect link 140 from one of the one or more transmitter entities 110 via at least one of the one or more DCS entities 130 to the receiver entity 120 is associated with one third m-identity 121 of the third set of m-identities. The steps 501, 502, 503 may be performed one after the other, in any order, or simultaneously. The method 500 further comprises a step 504 of generating, by a transmitter entity 110, atransmission signal 112 based on a respective unique m-sequence determined by the respectivefirst m-identity 111 of the transmitter entity 110. The method 500 also comprises a step 505 ofscattering, by a DCS entity 130, a signal 132 impinging onto the DCS entity 130 based on therespective second m-identity 131 of the DCS entity 130. The scattered signal 133 is based onthe respective second m-identity 131 of the DCS entity 130.Further, the method 500 comprises a step 506 of obtaining, by a receiver entity 120, a receivesignal 122, a step 507 of processing, by the receiver entity 120, the receive signal 122 based onone or more unique m-sequences, and a step 508 of identifying, by the receiver entity 120 as a result of the processing, whether zero or one or more of the one or more m-sequences arecomprised in the receive signal 122. Thereby, each of the one or more m-sequences isdetermined respectively by one of the one or more m-identities 111, 121, 131 of the fourth setof m-identities. The advantages of the solutions of this disclosure can be summarized as follows.^ The receiver entity 120 is enabled to identify surrounding active transmitter entities 110and passive DCS entities 130.^ Tracing and / or mapping transmitted signal trajectories becomes possible.^ The orthogonality observed after Fourier processing at the receiver entity 120 after oneor multiple DCS bounces can be preserved.^ A systematic way of code construction is enables, which is easy to extend.^ A post-processing based on the detected m-identities can be done at the receiver entity120 (e.g., to obtain SINR and / or to perform timing advance estimations).^ Discriminating interfering signals and enables applying efficient interference mitigationsolutions. Notably, in this disclosure, each of the transmitter entity 110, the receiver entity 120, the DCSentity 130, and the control entity 200 can be a stand-alone entity or device, and does notnecessarily have to be in the wireless communication system 100. Each entity, however, issuitable for being used in such a wireless communication system 100. That is, one embodimentof this disclosure provides a single transmitter entity 110, for instance, configured as describedwith respect to FIG. 1. Another embodiment of this disclosure provides a single receiver entity 120, for instance, configured as described with respect to FIG.1. Another embodiment of this disclosure provides a single DCS entity 130, for instance, configured as described with respectto FIG. 1. Another embodiment of this disclosure provides a single control entity 200, forinstance, configured as described with respect to FIG. 2. These stand-alone entities 110, 120,130, 200 are respectively reflected in the fifth, sixth, seventh and eighth aspect described in thesummary above, including the respective implementation forms. The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A wireless communication system (100) comprising one or more transmitter entities(110), one or more receiver entities (120), and one or more digitally controllable scatterer, DCS, entities (130), wherein: each transmitter entity (110) is provided with a respective first maximal length sequence identity (111), m-identity, of a first set of m-identities; each DCS entity (130) is provided with a respective second m-identity (131) of a second set of m-identities; each receiver entity (120) is provided with one or more m-identities of a fourth set of m- identities, the fourth set of m-identities comprising one or more of the first m-identities (111) and / or one or more of the second m-identities (131) and / or one or more third m- identities (121) of a third set of m-identities, wherein each indirect link (140) from one of the one or more transmitter entities (110) via at least one of the one or more DCS entities (130) to the receiver entity (120) is associated with one third m-identity (121) of the third set of m-identities; each transmitter entity (110) is configured to generate a signal (112) based on a respective unique maximal length sequence, m-sequence, determined by the respective first m- identity (111) of the transmitter entity (110); each DCS entity (130) is configured to scatter a signal (132) impinging onto the DCS entity (130) based on the respective second m-identity (131) of the DCS entity (130), wherein the scattered signal (133) is based on the respective second m-identity (131); and each receiver entity (120) is configured to: obtain a receive signal (122); process the receive signal (122) based on one or more unique m-sequences, each of the one or more m-sequences being determined respectively by one of the one or more m-identities (111, 121, 131) of the fourth set of m-identities; and identify, as a result of the processing, whether zero or one or more of the one ormore m-sequences are comprised in the receive signal (122).

2. The wireless communication system (100) according to claim 1, further comprising:a control entity (200) configured to determine at least one of the first set of m-identities, the second set of m-identities, the third set of m-identities, and the fourth set of m- identities.

3. The wireless communication system (100) according to claim 2, wherein the controlentity (200) is further configured to: provide at least one first m-identity (111) of the first set of m-identities to respectively at least one transmitter entity (110); and / or provide at least one second m-identity (131) of the second set of m-identities respectively to at least one DCS entity (130); and / or provide at least one m-identity (111, 121, 131) of the fourth set of m-identities to a receiver entity (120).

4. The wireless communication system (100) according to one of the claims 1 to 3, whereineach first m-identity (111) is associated with a respective transmitter entity (110) and is thus indicative, at a receiver entity (120), of a direct link (150) from the transmitter entity (110) to the receiver entity (120).

5. The wireless communication system (100) according to one of the claims 1 to 4, wherein:the third set of m-identities comprises one or more subsets of third m-identities (121); anda third m-identity (121) of a respective subset is associated with an indirect link (140) from one of the one or more transmitter entities (110) via a respective number of the oneor more DCS entities (130) to the receiver entity (120), the respective number being one or larger and different for the subsets.

6. The wireless communication system (100) according to one of the claims 1 to 5, wherein,if a signal (132) impinging onto the DCS entity (130) is based on a respective first m-identitythe respective first m-identity (111) and on the respective second m-identity (131) of the DCSentity (130).

7. The wireless communication system (100) according to one of the claims 1 to 6, whereinif a signal (132) impinging onto the DCS entity (130) is based on one or more respective second m-identities (131) of one or more other DCS entities (130), the scattered signal (133) is based on the one or more respective second m-identities (131) of the one or more other DCS entities (130) and on the respective second m-identity (131) of the DCS entity (130).

8. The wireless communication system (100) according to claims 1 to 7, wherein each DCSentity (130) comprises: a plurality of scattering elements, each scattering element having a controllable phase shift; and a DCS controller configured to control the scattering of the signal (131) impinging onto the DCS entity (130) by determining a respective phase shift configuration for the plurality of scattering elements based on the respective second m-identity (131) of the DCS entity (130).

9. The wireless communication system (100) according to claim 8, wherein the respectivephase shift configuration determined for each DCS entity (130) comprises a first phase shift configuration part and a second phase shift configuration part; wherein the first phase shift configuration is a function of the respective second m-identity(131) of the DCS entity (130), and the second phase shift configuration part is independent of the respective second m-identity (131).

10. The wireless communication system (100) according to one of the claims 1 to 9, whereineach receiver entity (120) is further configured to determine, based on the zero or one or more identified m-sequences comprised in the receive signal (122) at least one of: zero or one or more of the transmitter entities (110) from which at least a part of thereceive signal (122) originated;zero or one or more of the DCS entities (130) by which at least a part of the receive signal (122) was scattered; zero or one or more indirect links (140) over which at least a part of the receive signal (122) arrived at the receiver entity (120); and / or zero or one or more direct links (150) over which at least a part of the receive signal (122) arrived at the receiver entity (120).

11. The wireless communication system (100) according to one of the claims 1 to 10, whereineach receiver entity (120) is further configured to: correlate the receive signal (122) with each of a plurality of correlating signals, wherein each of the correlating signals is based on one of the one or more unique m-sequences that are determined by the m-identities (111, 121, 131) of the fourth set of m-identities.

12. The wireless communication system (100) according to claim 10 and 11, wherein thereceiver entity (120) is configured to determine the zero or one or more transmitter entities (110), and / or the zero or one or more DCS entities (130), and / or the zero or one or more indirect links (140), and / or the zero or one or more direct links (150), based on the result of the correlating with the plurality of correlating signals.

13. The wireless communication system (100) according to one of the claims 1 to 12, whereineach receiver entity (120) is further configured to perform a post-processing process comprising: determining a timing advance for each of one or more direct links (150) and / or for each of one or more indirect links (140); and / or estimating a signal-to-interference-plus-noise ratio, SINR, for the one or more direct links(150) and / or the one or more indirect links (140).

14. A method (500) for a wireless communication system (100) comprising one or moretransmitter entities (110), one or more receiver entities (120), and one or more digitally controllable scatterer, DCS, entities (130), the method (500) comprising:providing (501) each transmitter entity (110) with a respective first maximal length sequence identity, m-identity (111), of a first set of m-identities; providing (502) each DCS entity (130) with a respective second m-identity (131) of a second set of m-identities; providing (503) each receiver entity (120) with one or more m-identities of a fourth set of m-identities, the fourth set of m-identities comprising one or more of the first m- identities (111) and / or one or more of the second m-identities (131) and / or one or more third m-identities (121) of a third set of m-identities, wherein each indirect link (140) from one of the one or more transmitter entities (110) via at least one of the one or more DCS entities (130) to the receiver entity (120) is associated with one third m-identity (121) of the third set of m-identities;generating (504), by a transmitter entity (110), a signal (112) based on a respective unique maximal length sequence, m-sequence, determined by the respective first m-identity (111) of the transmitter entity (110); scattering (505), by a DCS entity (130), a signal (132) impinging onto the DCS entity (130) based on the respective second m-identity (131) of the DCS entity (130), wherein the scattered signal (133) is based on the respective second m-identity (131) of the DCS entity (130); obtaining (506), by a receiver entity (120), a receive signal (122); processing (507), by the receiver entity (120), the receive signal (122) based on one or more unique m-sequences, each of the one or more m-sequence being determined respectively by one of the one or more m-identities (111, 121, 131) of the fourth set of m-identities; and identifying (508), by the receiver entity (120) as a result of the processing, whether zero or one or more of the one or more m-sequences are comprised in the receive signal (122).

15. A computer program comprising instructions which, when the program is executed by acomputer of the transmitter entity (110), the DCS entity (130), or the receiver entity (120),respectively, cause the computer to perform the steps of the transmitter entity (110), the DCSentity (130), or the receiver entity (120) of the method (500) according claim 14.

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