Determining information for tracking a user equipment

Abstract

According to an example aspect of the present invention, there is provided receiving, by an apparatus, a first direct transmission from a wireless device in at least one first downlink transmission time period, receiving, by the apparatus, in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked, determining, by the apparatus, information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device, determining, by the apparatus, information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment and transmitting, by the apparatus, said information about the second wireless channel to the wireless device.

Description

DETERMINING INFORMATION FOR TRACKING A USER EQUIPMENTFIELD

[0001] Various example embodiments relate to determining information for tracking a user equipment.BACKGROUND

[0002] Tracking a User Equipment, UE, may be beneficial, or even mandatory, for various applications in wireless communication networks. For example, in case of cellular communication networks Radio Frequency, RF, signals may be used to track UEs. There is a need to provide enhanced methods, apparatuses and computer programs related to tracking of UEs, at least in cellular communication networks, such as in networks operating according to 3rd Generation Partnership Project, 3 GPP, standards. Such enhancements may also be beneficial in other wireless communication networks.SUMMARY

[0003] According to some aspects, there is provided the subject-matter of the independent claims. Some example embodiments are defined in the dependent claims.

[0004] The scope of protection sought for various example embodiments of the invention is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various example embodiments of the invention.

[0005] According to a first aspect of the present invention, there is provided an apparatus comprising at least one processing core, at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to receive a first direct transmission from a wireless device in at least one first downlink transmission time period, receive in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked, determine information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatusand the wireless device, determine information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment and transmit said information about the second wireless channel to the wireless device.

[0006] Example embodiments of the first aspect may comprise at least one feature from the following bulleted list or any combination of the following features:• wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to receive the first direct transmission in the at least one first downlink transmission time period, and the second direct transmission and the indirect transmission in the at least one second downlink transmission time period, within a channel coherence time of the first wireless channel;• wherein the at least one first downlink transmission time period for the first direct transmission and the at least one second downlink transmission time period for the second direct transmission and indirect transmission are configured in relation with a time selectivity of the first wireless channel;• wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to receive the first direct transmission in the at least one first downlink transmission time period, and the second direct transmission and indirect transmission in the at least one second downlink transmission time period, within a sampling time of the apparatus;• wherein the first direct transmission and the second direct transmission are beamformed to cover the apparatus and the user equipment;• wherein the apparatus is another user equipment and the wireless device is a wireless network node;• wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to receive, from the wireless device, a configuration for receiving transmissions in the at least one first downlink transmission time period and in the at least one second downlink transmission time period.

[0007] According to a second aspect of the present invention, there is provided an apparatus comprising at least one processing core, at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to receive a first direct transmission from a wireless device in at least one first uplink transmission time period, receive in at least one second uplink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked, determine information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device, determine information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the apparatus and the user equipment and track the user equipment using said information about the second wireless channel.

[0008] Example embodiments of the second aspect may comprise at least one feature from the following bulleted list or any combination of the following features:• wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to receive the first direct transmission in the at least one first uplink transmission time period, and the second direct transmission and indirect transmission in the at least one second uplink transmission time period, within a channel coherence time of the first wireless channel;• wherein the at least one first uplink transmission time period for the first direct transmission and the at least one second uplink transmission time period for the second direct transmission and the indirect transmission are configured in relation with a time selectivity of the first channel;• wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to receive the first direct transmission in the at least one first uplink transmission time period, and the second direct transmission and the indirect transmission in the at least one second uplink transmission time period, within a sampling time of the apparatus;• wherein the first direct transmission and the second direct transmission are beamformed to cover the wireless device and the user equipment;• wherein the apparatus is a wireless network node and the wireless device is another user equipment;• wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to transmit, to the wireless device, a configuration for transmitting during the at least one first uplink transmission time period and the at least one second uplink transmission time period;• wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to receive information about a third channel, wherein the third channel is between the wireless device and the user equipment to be tracked and determine said information about the second wireless channel based on said information about the third channel.

[0009] According to a third aspect of the present invention, there is provided a method, comprising receiving, by an apparatus, a first direct transmission from a wireless device in at least one first downlink transmission time period, receiving, by the apparatus, in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked, determining, by the apparatus, information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device, determining, by the apparatus, information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment and transmitting, by the apparatus, said information about the second wireless channel to the wireless device.

[0010] According to a fourth aspect of the present invention, there is provided a method, comprising receiving, by an apparatus, a first direct transmission from a wireless device in at least one first uplink transmission time period, receiving, by the apparatus, in at least one second uplink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked, determining, by the apparatus, information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device, determining,by the apparatus, information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the apparatus and the user equipment and tracking, by the apparatus, the user equipment using said information about the second wireless channel.

[0011] According to a fifth aspect of the present invention, there is provided an apparatus, comprising means for receiving a first direct transmission from a wireless device in at least one first downlink transmission time period, means for receiving in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked, means for determining information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device, means for determining information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment and means for transmitting said information about the second wireless channel to the wireless device.

[0012] According to a sixth aspect of the present invention, there is provided an apparatus, comprising means for receiving a first direct transmission from a wireless device in at least one first uplink transmission time period, means for receiving in at least one second uplink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked, means for determining information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device, means for determining information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the apparatus and the user equipment and means for tracking the user equipment using said information about the second wireless channel.

[0013] According to a seventh aspect of the present invention, there is provided a non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the first method. According to an eighth aspect of the present invention, there is provided a non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the second method.

[0014] According to a ninth aspect of the present invention, there is provided a computer program comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the first method. According to a tenth aspect of the present invention, there is provided a computer program comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the second method.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 illustrates an example of a network scenario in accordance with at least some example embodiments;

[0016] FIG. 2 illustrates a first signalling graph in accordance with at least some example embodiments;

[0017] FIG. 3 illustrates a second signalling graph in accordance with at least some example embodiments;

[0018] FIG. 4 illustrates a third signalling graph in accordance with at least some example embodiments;

[0019] FIG. 5 illustrates an example apparatus capable of supporting at least some example embodiments;

[0020] FIG. 6 illustrates a flow graph of a first method in accordance with at least some example embodiments;

[0021] FIG. 7 illustrates a flow graph of a second method in accordance with at least some example embodiments.EXAMPLE EMBODIMENTS

[0022] Embodiments of the present disclosure provide enhancements for tracking User Equipments, UEs. More specifically, embodiments of the present disclosure provide enhancements for tracking UEs in a scenario, wherein a UE to be tracked does not transmit tracking signals to a wireless network node that is configured to track the UE. The UE to be tracked may forward and / or reflect Radio Frequency, RF, signals though, thereby generating an indirect transmission. The wireless network node may then receive or determine information about a channel between the UE to be tracked and the wireless network node, based at least on the indirect transmission. Hence, tracking of the UE is enabled, without requiring network capacity to be allocated for dedicated tracking signals. Instead, the forwarded and / or reflected RF signals, which may carry data, may be used for tracking.

[0023] FIG. 1 illustrates an example of a network scenario in accordance with at least some example embodiments. According to the example scenario of FIG. 1, there may be a communication system, which comprises primary UE 110, secondary UE 112, wireless network node 120 and core network element 130. Primary UE 110 and secondary UE 112 may be connected to wireless network node 120, and also to each other, via air interface 115. The connection(s) between UEs and / or between UE and node 120 may be bidirectional or in some cases at least some of the connect! on(s) may be unidirectional. For instance, in some examples, secondary UE 112 may be configured for receiving information from the wireless network node 120, but not transmit information to wireless network node 120. UEs 110 and 112 may be connected to wireless network node 120, and possibly each other, for example by using multiple beams, either simultaneously or one at a time. That is, air interface 115 may be a beam-based air interface.

[0024] Even though the terms “primary UE” and “secondary UE” are used as examples, primary UE 110 may be referred to as a first UE and secondary UE 112 may be referred to as a second UE as well. In some example embodiments, secondary UE 112 may be referred to as a UE and primary UE 110 may be referred to as another UE. In some example embodiments, secondary UE 112 may be referred to as a tethered UE. Alternatively, or in addition, secondary UE 112 may be configured as an Intelligent Reflective Surface, IRS.

[0025] At least in case of downlink transmissions, primary UE 110 may be referred to as an apparatus and wireless network node 120 may be referred to as a wireless device. At least in case of uplink transmissions, wireless network node 120 may be referred to as an apparatus and primary UE 110 may be referred to as a wireless device.

[0026] UEs 110 and 112 may comprise, for example, a smartphone, a cellular phone, a Machine-to-Machine, M2M, node, Machine-Type Communications, MTC, node, an Internet of Things, loT, node (e.g., loT device), a car telemetry unit, a laptop computer, a tablet computer or, indeed, any kind of suitable wireless terminal. For example, primary UE 110 may be a cellular phone and secondary UE 112 may be secondary device, such as smart glasses or a wrist watch, connected to primary UE 110. In an embodiment, primary UE 112 may be a RedCap UE. In an embodiment, primary UE 110 may be a non-RedCap UE and secondary UE 112 may be a RedCap UE. Wireless network node 120 may be considered as a serving node for UEs 110 and 112, and one cell of wireless network node 120 may be a serving cell for UEs 110 and 112.

[0027] Primary UE 110 may be configured to transmit and receive RF signals from wireless network node 120 and secondary UE 112. Secondary UE 112 may have a capability to forward and / or reflect RF signals coming from primary UE 110 to wireless network node 120, to enable reception of an indirect transmission from primary UE 110 at wireless network node 120. Secondary UE 112 may have a capability to forward and / or reflect RF signals coming from wireless network node 120 to primary UE 110, to enable reception of an indirect transmission from wireless network node 120 at primary UE 110.

[0028] Air interface between UEs 110 and 112, and wireless network node 120, may be configured in accordance with a Radio Access Technology, RAT, which both UE 110 and wireless network node 120 are configured to support. Examples of cellular RATs include Long Term Evolution, LTE, New Radio, NR, which may also be known as fifth generation, 5G, radio access technology and MulteFire.

[0029] For example in the context of LTE, wireless network node 120 may be referred to as eNB while wireless network node 120 may be referred to as gNB in the context of NR. In some example embodiments, wireless network node 120 may be referred to as a Transmission and Reception Point, TRP, or control multiple TRPs that may be co-located or non-co-located. In any case, example embodiments of the present disclosure are not restricted to any particular wireless technology. Instead, exampleembodiments may be exploited in any wireless communication system, wherein it would be beneficial to track UEs, such as tethered UEs, that are not be able to actively transmit RF signals.

[0030] Example embodiments of the present disclosure may be related to, e.g., Joint / Integrated Communication and Sensing, J / ICAS, technology. Such technology may be exploited at least in 5G and 6G networks. In case of J / ICAS, RF signals intended for data transfer may be used to also track secondary UE 112. Tracking may comprise detecting and locating secondary UE 112. Secondary UE 112 may be a forwarding one (which detects the incoming signal and forwards it). The key benefit of J / ICAS is its non- invasiveness.

[0031] Sensing and communication may share the same frequency band and hardware. As wireless communication technologies, such as massive Multiple-Input Multiple-Output, MIMO, evolves with more antenna elements and wider bandwidth in higher frequency bands, e.g., mm-wave bands, the technologies may become reliant on increasingly more specific and accurate assistance information. Such assistance information may comprise for example distance (range), angle, instantaneous velocity, and area of various objects, like UEs. Meanwhile, wireless sensing technologies aim at acquiring information about a remote object without physical contact. The sensing data of the object and its surrounding may then be utilized for analysis so that meaningful information about the object and its characteristics may be obtained with high resolution and reliable accuracy. Leveraging the strengths of wireless sensing technologies is expected to be advantageous to the development of future wireless communication technologies and hence, the integration of sensing and communication is needed.

[0032] Sensing services may be beneficial at least for intelligent transportation, aviation, enterprise, smart city, smart home, smart factories, consumer applications, and public sector. Meanwhile, the sensing wireless system, that relies on the same wireless communication system and infrastructure, may offer sensing information. Said sensing information may be utilized to assist the wireless communication functionalities, such as radio resource management, interference mitigation, beam management, mobility, etc. A higher efficiency for both sensing services and sensing assisted communications may be enabled when the wireless sensing and communication are integrated in the same wireless channel or environment.

[0033] Tethered UEs may be used for example in tethered XR architectures, wherein UEs may cooperate on a single service with potentially all having connection to wireless network node 120, and between themselves as well. The UE interconnectivity may be a 3GPP sidelink but it may also be Wireless Local Area Network, WLAN, or, for example, some other non-3GPP connection. As another example, in industrial loT larger machinery may have multiple UEs integrated into its body serving the various autonomous functions or simply redundancy.

[0034] In case of J / ICAS, for example primary UE 110 or wireless network node 120 may need to simultaneously perform data transfer (uplink, downlink or sidelink) and track one or more targets (e.g., other UEs, pedestrians, moving objects etc.). The data transfer and tracking of targets may be performed using the same time, frequency, and space resources. A challenge is how to enable simultaneous data transfer and tracking of targets.

[0035] Embodiments of the present disclosure therefore enable simultaneous data transfer and tracking of targets, for example in a tethered XR scenario. For example, in some embodiments, primary UE 110 receiving downlink data from wireless network node 120 may also track tethered XR glasses UE, such as secondary UE 112. Primary UE 110 may track the tethered UE while primary UE 110 is receiving downlink data from wireless network node 120. Even though slots are used in various example embodiments, embodiments of the present disclosure may be applied with any transmission time periods (e.g. slot may be one example of transmission time period) in general, i.e., not limited to slots. That is, the slots may not necessarily refer to NR slots. Instead, the slots may refer to just a few symbols, like a set of symbols, or transmission opportunities.

[0036] In some example embodiments, wireless network node 120 may configure a subframe, such as a J / ICAS subframe. The subframe may comprise interleaving first downlink slots (D-slots) and second downlink slots, such as downlink relay slots (DR- slots). The first downlink slots (D-slots) may carry downlink signals while wireless network node 120 may continue a downlink transmission during the second slots (DR- slots), wherein secondary UE 112 may forward the downlink transmission during the second slots to primary UE 110.

[0037] Primary UE 110 may be configured to receive a first direct transmission from wireless network node 120 in at least one downlink slot (e.g. one or more first slots,may be referred to as one or more D-slots). Primary UE 110 may be also configured to receive in at least one other downlink slot (e.g. one or more second slots, can be referred to as one or more DR-slots) a second direct transmission from wireless network node 120 and an indirect transmission of the second direct transmission of wireless network node 120 via secondary UE 112 to be tracked. For example, primary UE 110 may receive a hybrid DL subframe comprising the D-slot(s) and the DR-slot(s) and use the D-slot(s) to learn the response of the direct, first downlink channel, i.e., the channel between primary UE 110 and wireless network node 120. Primary UE 110 may, after having learned the direct, first channel, use said learning and the DR-slots to learn the response of the channel between secondary UE 112 and wireless network node 120. A prior knowledge of the tethered channel, i.e., the channel between primary UE 110 and secondary UE 112, may be assumed. Primary UE 110 may then report, to wireless network node 120, information about the channel between secondary UE 112 and wireless network node 120. In some example embodiments, secondary UE 112 may be configured to relay the DR-slots to primary UE 110, e.g., amplify and forward the transmissions of RF signals in the DR- slots.

[0038] As used in this disclosure, receiving a slot or slots may refer to receiving information or data (e.g. receiving transmission or transmissions) transferred in the slot or slot from transmitting entity by receiving entity.

[0039] Wireless network node 120 may then use said information about the channel between secondary UE 112 and wireless network node 120, i.e., the indirect DL channel report, to track secondary UE 112.

[0040] In some example embodiments, primary UE 110 may perform channel estimation to determine information (Cl) about a first channel, wherein the first channel is between primary UE 110 and wireless network node 120. Said information about the first channel may comprise everything needed for immediate data decoding but also optional information, like angle of arrival. For example the full estimated impulse response of the first channel may be reported to wireless network node 120. Primary UE may store said information about the first channel locally for use in the second, DR slot. For example primary UE 110 may store the estimated channel impulse response.

[0041] In the second, DR slot primary UE 110 may receive a superposition (C) of the second direct transmission (from wireless network node 120 to primary UE 110directly) and the indirect transmission of the second direct transmission via secondary UE 112. Then, primary UE 110 may determine the indirect path (C2=C-C1), wherein the indirect path comprises a second channel, wherein the second channel is between wireless network node 120 and secondary UE 112, and a third channel, wherein the third channel is between primary UE 110 and secondary UE 112. Hence, C2 may be a channel impulse response but a composite one as it includes information about the second and third channels. Primary Ue 110 may know the third channel (Cth) and hence the unknown channel would be a fourth channel (Ctrack), wherein the fourth channel is between secondary UE 112 and wireless network node 120. Primary UE 110 may hence determine information about the second channel (Ctrack=C-Cl-Cth). Said information about the second channel may be an impulse response, comprising for example the delay information. Alternatively, or in addition, said information about the second channel may comprise an angle of arrival and / or an angle of departure.

[0042] In some example embodiments, the procedure may be applied to uplink similarly, wherein wireless network node 120 may receive data from primary UE 110 while wireless network node 120 may simultaneously track secondary UE 112.

[0043] FIG. 2 illustrates a first signalling graph in accordance with at least some example embodiments. On the vertical axes are disposed, from the left to the right, wireless network node 120, primary UE 110 and secondary UE 112 of FIG. 1. Time advances from the top towards the bottom. In the example of FIG. 2, primary UE 110 may be referred to as an apparatus and wireless network node 120 may be referred to as a wireless device.

[0044] At step 202, wireless network node 120 may trigger a communication session, such as a J / ICAS, towards primary UE 110. At step 204, wireless network node 120 may transmit a configuration to primary UE 110, wherein the configuration may be for receiving the at least one first downlink slot (D-slot) and the at least one second downlink slot (DR-slot).

[0045] At step 206, wireless network node 120 may transmit a configuration to secondary UE 112, the configuration comprising or indicating a strategy or rule to forward a transmission in the at least one second slot (i.e. DR-slot) to primary UE 110, i.e., to forward the DR-slots originally intended for primary UE 110. In some exampleembodiments, primary UE 110 may perform tethered link estimation, i.e., determine information about a channel between primary UE 110 and secondary UE 112.

[0046] At step 208, wireless network node 120 may transmit a first direct transmission to primary UE 110 in the at least one first slot (D-slot). At step 210, the first direct transmission may also reach secondary UE 112. At step 212, secondary UE 112 may take no action and remain quiet (e.g., determine not to take action and to remain quiet). Secondary UE 112 may receive data of its own in this slot though, independent of the J / ICAS session. For example, the configuration received at step 206 by the secondary UE 112 may indicate the secondary UE 112 to not forward the transmission received in the at least one first slot (D-slot). Thus, the secondary UE 112 may not forward the first direct transmission to the UE 110 based on the configuration. For example, the secondary UE 112 may determine not to forward the first direct transmission based on the configuration (of step 206).

[0047] At step 214, primary UE 110 may determine information about a first wireless channel (or simply, first channel) based on the first direct transmission, wherein the first wireless channel is between primary UE 110 and wireless network node 120. A channel estimation procedure may be performed by primary UE 110 and hence, primary UE 110 may learn or update its knowledge or information on the first wireless channel between the primary UE 110 and the wireless network node 120. I.e. channel estimation procedure may be performed to obtain information on the first wireless channel based on the first direct transmission.

[0048] At step 216, wireless network node 120 may transmit in at least one second downlink slot (DR-slot) a second direct transmission. At step 218, the second direct transmission may also reach secondary UE 112. At step 220, secondary UE 112 may activate relay functionality. At step 222, secondary UE 112 may relay the second direct transmission to primary UE 110. Hence, primary UE 110 may receive, via secondary UE 112, an indirect transmission of wireless network node 120. The at least one first downlink slot for the first direct transmission and the at least one second downlink slot for the second direct and indirect transmissions may be received, by primary UE 110, within a channel coherence time.

[0049] At step 224, primary UE 110 may determine information about a second wireless channel (or simply, second channel) based on the determined first wirelesschannel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between secondary UE 112 and wireless network node 120. Primary UE 110 may hence use the information from step 214 along with prior knowledge of a third channel, wherein the third channel is between primary UE 110 and secondary UE 112 to decode the jointly received signal from the direct link with wireless network node 120 and indirect link from wireless network node 120 to secondary UE 112, and from secondary UE 112 further to primary UE 110. The extracted information is about the second channel, between wireless network node 120 and secondary UE 112, which is the required tracking information.

[0050] Information about a channel may be a response of the channel in frequency or time domains and said information may be used to extract an angle of arrival / departure of the signal, propagation delay over the direct path and / or multipath information. These may in turn be compared with the past estimates and computed differences between: angle of arrivals at two different instances, angle of departures at two instances, delays at two instances. Then, using the displacement information (inferred from the differential delay), or the rotation information (inferred from the differential angle of arrival), a change in location and orientation of secondary UE 112 may be updated.

[0051] At step 226, primary UE 110 may transmit said information about the second wireless channel to wireless network node 120. Alternatively, or in addition, primary UE 110 may exploit said information about the second wireless channel itself.

[0052] In some example embodiments, wireless network node 120 may configure both, primary UE 110 and secondary UE 112, with information about the at least one first slot (D-slot) and the at least one second slot (DR-slot). As the determination at step 224 depends on prior knowledge of the at least one first slot (D-slot) measured at step 214, wireless network node 120 may configure the at least one first slot and the at least one second slot within a channel coherence time of the first channel. For example, primary UE 110 and secondary UE 112 may be paired XR devices in proximity of each other and hence, channel parameters may be correlated. That is, wireless network node 120 may ensure, or at least increase, the success of said determination, at step 224, by configuring the at least one first slot and the at least one second slot close enough in time to ensure the first channel may be considered quasi-static. That is, the at least one first uplink transmission time period for the first direct transmission and the at least one second uplinktransmission time period for the second direct transmission and the indirect transmission may be configured in relation with a time selectivity of the first channel.

[0053] In some example embodiments, the at least one first slot and the at least one second slot may be two distinct Demodulation Reference Signal, DM-RS, transmissions (or DM-RS equivalence in 6G). For example, in 5G, DM-RS configuration may have multiple instances within a 5G slot. This may be done for high-speed scenarios and fast varying channels. Such DM-RS transmissions may then be in different symbols within a 5G slot.

[0054] FIG. 3 illustrates a second signalling graph in accordance with at least some example embodiments. On the vertical axes are disposed, from the left to the right, wireless network node 120, primary UE 110 and secondary UE 112 of FIG. 1. Time advances from the top towards the bottom. In the example of FIG. 3, the configuration of the at least one second slot (DR-slots) for secondary UE 112 may be delegated by wireless network node 120 to primary UE 110.

[0055] Step 302 may correspond to step 202 of FIG. 2. That is, at step 302, wireless network node 120 may trigger a communication session, such as a J / ICAS, towards primary UE 110. At step 304, wireless network node 120 may transmit a configuration to primary UE 110, the configuration comprising the at least one first downlink slot (D-slot), but not the at least one second downlink slot (DR-slot). In some example embodiments, wireless network node 120 may give explicit instructions to primary UE 110 to configure secondary UE 112 with the at least one second downlink slot (DR-slot).

[0056] At step 306, primary UE 110 may transmit a configuration to secondary UE 112, the configuration comprising the at least one other downlink slot (DR-slot), but not the at least one downlink slot (D-slot). In some example embodiments, primary UE 110 may perform tethered link estimation, i.e., determine information about a channel between primary UE 110 and secondary UE 112. Steps 308 - 312 may correspond to steps 208 - 212 of FIG. 2, respectively. I.e. step 308 may correspond to step 208; step 310 may correspond to step 210; and step 312 may correspond to step 212. More specifically, at step 308, wireless network node 120 may transmit a first direct transmission to primary UE 110 in the at least one first slot (D-slot). At step 310, the first direct transmission may also reach secondary UE 112. At step 312, secondary UE 112may take no action and remain quiet (e.g., determine not to take action and to remain quiet). Step 314 may comprise steps 214 - 226.

[0057] FIG. 4 illustrates a third signalling graph in accordance with at least some example embodiments. On the vertical axes are disposed, from the left to the right, wireless network node 120, primary UE 110 and secondary UE 112 of FIG. 1. Time advances from the top towards the bottom. In the example of FIG. 4, the quasi-static nature of the channel may be ensured from wireless network node 120 to primary UE 110 and secondary UE 112.

[0058] In some example embodiments, the tethered link part of the relay path (a third channel, wherein the third channel is between primary UE 110 and secondary UE 112) may be assumed to be low delay and known gain. The procedure may be triggered upon J / ICAS configuration or determined and updated independent of the JCAS configuration.

[0059] The tethered link may be expected to have a lot longer coherence time. However, it is not a requirement. The second, DR slots may need to be within the coherence time of the first channel (the channel between wireless network node 120 and primary UE 110) and tethered link estimation (whenever that might be) and the second, DR slots may have to be within the coherence time of the third channel, i.e., the tethered link. Hence, the third, tethered channel may have a shorter coherence time than the first channel as long as the estimation is done within the coherence time of the first channel.

[0060] Steps 402 - 404 may comprise steps 202 - 206 of FIG. 2, respectively. I.e. step 402 may correspond to step 202; step 403 may correspond to step 204; and step 404 may correspond to step 206. More specifically, at step 402, wireless network node 120 may trigger a communication session, such as a J / ICAS, between primary UE 110 and secondary UE 112. At step 403, wireless network node 120 may transmit a configuration to primary UE 110, wherein the configuration may be for receiving the at least one first downlink slot (D-slot) and the at least one second downlink slot (DR-slot). At step 404, wireless network node 120 may transmit the configuration to secondary UE 112.

[0061] At step 406, primary UE 110 may determine the tethered link channel, i.e., determine information about a third channel, wherein the third channel is between primary UE 110 and secondary UE 112. Steps 408 - 412 may correspond to steps 208 -212 of FIG. 2, respectively. That is, at step 408, wireless network node 120 may transmit a first direct transmission to primary UE 110 in the at least one first slot (D-slot). At step 410, the first direct transmission may also reach secondary UE 112. At step 412, secondary UE 112 may take no action and remain quiet (e.g., determine not to take action and to remain quiet). Step 414 may comprise steps 214 - 226.

[0062] Alternatively, in some example embodiments, the third, tethered link channel estimation may be performed during the optional configuration of secondary UE 112 by primary UE 110, at step 306 of FIG. 3.

[0063] In some example embodiments, the configuration for slots (D- and DR- slots) may also include other configuration parameters enabling or improving the performance. For example, typical communication between wireless network node 120 and primary UE 110 may be ongoing with high directivity beams. Power collected from secondary UE 112 may be too low if high gain beamforming is used towards primary UE 110. Therefore, in some example embodiments, a wide beam may be selected to cover primary UE 110 and secondary UE 112 at the time of the transmission of the slots (D- and DR-slots), to ensure meaningful power levels at the time of samples collection.

[0064] That is, the first direct transmission and the second direct transmission may be beamformed to cover primary UE 110 and secondary UE 112. The first direct transmission and the second direct transmission may be configured to have sufficient power at both UEs (to decode / re-transmit). Sufficiency of power may depend, e.g., on path losses, RF capabilities etc. The aim may be that the used beam should not result in zero power at primary UE 110 or secondary UE 110. As the first wireless channel between primary UE 110 and wireless network node 120 may be learned during the at least one first slot (D-slot) and used later on, a requirement may be that the first wireless channel stays the same for the at least one second slot (DR-slot). A change of beams form wireless network node 120 may lead to a different perceived channel even if the at least one first slot and the at least one second slot are within the channel coherence time of the first channel. Hence, it may be forbidden (or at the very least restricted) to change beams for transmissions in the at least one first slot and the at least one second slot.

[0065] In some example embodiments, the relay operation at secondary UE 112 may be within the sampling time at primary UE 110. The third, tethered link delay may be significantly smaller than the delay spread from wireless network node 120 to primaryUE 110 and secondary UE 112, so that it may be considered insignificant. This ensures reception within the sampling time of primary UE 110. Such fast relaying may be achieved with pure RF relay functionality, i.e., amplify and forward. Some additional processing at secondary UE 112 may be added though.

[0066] In some example embodiments, similar procedures may be applied for uplink. In such a case, wireless network node 120 may receive a first direct transmission from primary UE 110 in at least one first uplink slot. Wireless network node 120 may also receive in at least one second uplink slot a second direct transmission from primary UE 110 and an indirect transmission of the second direct transmission of primary UE 110 via secondary UE 112. Wireless network node 120 may then determine information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between wireless network node 120 and primary UE 110. Wireless network node 120 may further determine information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless network node 120 and secondary UE 112. Wireless network node 120 may track the user equipment using said information about the second wireless channel. In case of uplink, wireless network node 120 may be referred to as an apparatus and primary UE 110 may be referred to as a wireless device.

[0067] In some example embodiments, primary UE 110 may transmit to wireless network node information about a third channel, wherein the third channel is between primary UE 110 and secondary UE 112. Wireless network node 120 may then determine said information about the second wireless channel based on said information about the third channel.

[0068] FIG. 5 illustrates an example apparatus capable of supporting at least some example embodiments. Illustrated is device 500, which may comprise, for example, primary UE 110, secondary UE 112 or wireless network node 120, or a control device configured to control the functioning thereof, possibly when installed therein. Comprised in device 500 is processor 510, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multicore processor comprises more than one processing core. Processor 510 may comprise, in general, a control device. Processor 510 may comprise more than one processor.Processor 510 may be a control device. A processing core may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Steamroller processing core produced by Advanced Micro Devices Corporation. Processor 510 may comprise at least one Qualcomm Snapdragon and / or Intel Atom processor. Processor 510 may comprise at least one application-specific integrated circuit, ASIC. Processor 510 may comprise at least one field-programmable gate array, FPGA. Processor 510 may be means for performing method steps in device 500. Processor 510 may be configured, at least in part by computer instructions, to perform actions.

[0069] A processor may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein. As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor s) or a portion of a microprocessor s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0070] 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.

[0071] Device 500 may comprise memory 520. Memory 520 may comprise random-access memory and / or permanent memory. Memory 520 may comprise at least one RAM chip. Memory 520 may comprise solid-state, magnetic, optical and / orholographic memory, for example. Memory 520 may be at least in part accessible to processor 510. Memory 520 may be at least in part comprised in processor 510. Memory 520 may be means for storing information. Memory 520 may comprise computer instructions that processor 510 is configured to execute. When computer instructions configured to cause processor 510 to perform certain actions are stored in memory 520, and device 500 overall is configured to run under the direction of processor 510 using computer instructions from memory 520, processor 510 and / or its at least one processing core may be considered to be configured to perform said certain actions. Memory 520 may be at least in part comprised in processor 510. Memory 520 may be at least in part external to device 500 but accessible to device 500.

[0072] Device 500 may comprise a transmitter 530. Device 500 may comprise a receiver 540. Transmitter 530 and receiver 540 may be configured to transmit and receive, respectively, information in accordance with at least one cellular or non-cellular standard. Transmitter 530 may comprise more than one transmitter. Receiver 540 may comprise more than one receiver. Transmitter 530 and / or receiver 540 may be configured to operate in accordance with Global System for Mobile communication, GSM, Wideband Code Division Multiple Access, WCDMA, Long Term Evolution, LTE, and / or 5G / NR standards, for example.

[0073] Device 500 may comprise a Near-Field Communication, NFC, transceiver 550. NFC transceiver 550 may support at least one NFC technology, such as Bluetooth, Wibree or similar technologies.

[0074] Device 500 may comprise User Interface, UI, 560. UI 560 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 500 to vibrate, a speaker and a microphone. A user may be able to operate device 500 via UI 560, for example to accept incoming telephone calls, to originate telephone calls or video calls, to browse the Internet, to manage digital files stored in memory 520 or on a cloud accessible via transmitter 530 and receiver 540, or via NFC transceiver 550, and / or to play games.

[0075] Device 500 may comprise or be arranged to accept a user identity module 570. User identity module 570 may comprise, for example, a Subscriber Identity Module, SIM, card installable in device 500. A user identity module 570 may comprise information identifying a subscription of a user of device 500. A user identity module 570may comprise cryptographic information usable to verify the identity of a user of device 500 and / or to facilitate encryption of communicated information and billing of the user of device 500 for communication effected via device 500.

[0076] Processor 510 may be furnished with a transmitter arranged to output information from processor 510, via electrical leads internal to device 500, to other devices comprised in device 500. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory 520 for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise processor 510 may comprise a receiver arranged to receive information in processor 510, via electrical leads internal to device 500, from other devices comprised in device 500. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 540 for processing in processor 510. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver.

[0077] Device 500 may comprise further devices not illustrated in FIG. 5. For example, where device 500 comprises a smartphone, it may comprise at least one digital camera. Some devices 500 may comprise a back-facing camera and a front-facing camera, wherein the back-facing camera may be intended for digital photography and the frontfacing camera for video telephony. Device 500 may comprise a fingerprint sensor arranged to authenticate, at least in part, a user of device 500. In some example embodiments, device 500 lacks at least one device described above. For example, some devices 500 may lack a NFC transceiver 550 and / or user identity module 570.

[0078] Processor 510, memory 520, transmitter 530, receiver 540, NFC transceiver 550, UI 560 and / or user identity module 570 may be interconnected by electrical leads internal to device 500 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device 500, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the example embodiment, various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the example embodiments.

[0079] FIG. 6 is a flow graph of a first method in accordance with at least some example embodiments.

[0080] The first method may comprise, at step 610, receiving, by an apparatus, a first direct transmission from a wireless device in at least one first downlink transmission time period. The first method may also comprise, at step 620, receiving, by the apparatus, in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked. The first method may further comprise, at step 630, determining, by the apparatus, information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device. The first method may also comprise, at step 640, determining, by the apparatus, information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment. Finally, the first method may comprise, at step 650, transmitting, by the apparatus, said information about the second wireless channel to the wireless device. The apparatus may be primary UE 110 and the wireless device may be wireless network node 120.

[0081] FIG. 7 is a flow graph of a second method in accordance with at least some example embodiments.

[0082] The second method may comprise, at step 710, receiving, by an apparatus, a first direct transmission from a wireless device in at least one first uplink transmission time period. The second may also comprise, at step 720, receiving, by the apparatus, in at least one second uplink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked. The second method may further comprise, at step 730, determining, by the apparatus, information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device. The second method may also comprise, at step 740, determining, by the apparatus, information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the apparatus and the user equipment. Finally, the second method may comprise, at step 750, tracking, by the apparatus, the user equipment using said information about the second wireless channel.

[0083] It is to be understood that the example embodiments disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular example embodiments only and is not intended to be limiting.

[0084] Reference throughout this specification to one example embodiment or an example embodiment means that a particular feature, structure, or characteristic described in connection with the example embodiment is included in at least one example embodiment. Thus, appearances of the phrases “in one example embodiment” or “in an example embodiment” in various places throughout this specification are not necessarily all referring to the same example embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0085] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various example embodiments and examples may be referred to herein along with alternatives for the various components thereof. It is understood that such example embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations.

[0086] In an example embodiment, an apparatus, such as, for example, primary UE 110, secondary UE 112 or wireless network node 120, may comprise means for carrying out the example embodiments described above and any combination thereof.

[0087] In an example embodiment, a computer program may be configured to cause a method in accordance with the example embodiments described above and any combination thereof. In an example embodiment, a computer program product, embodied on a non-transitory computer readable medium, may be configured to control a processorto perform a process comprising the example embodiments described above and any combination thereof.

[0088] In an example embodiment, an apparatus, such as, for example, primary UE 110, secondary UE 112 or wireless network node 120, may comprise at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform the example embodiments described above and any combination thereof.

[0089] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of example embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the disclosure can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure.

[0090] While the forgoing examples are illustrative of the principles of the example embodiments in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the disclosure. Accordingly, it is not intended that the disclosure be limited, except as by the claims set forth below.

[0091] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0092] At least some example embodiments find industrial application in cellular communication networks, for example in 3 GPP networks.ACRONYMS LIST3GPP 3rd Generation Partnership ProjectBS Base StationDM-RS Demodulation Reference SignalGSM Global System for Mobile communication loT Internet of ThingsIRS Intelligent Reflective SurfaceJ / ICAS Joint / Integrated Communication and SensingLTE Long-Term EvolutionM2M Machine-to-MachineMIMO Multiple-Input Multiple-OutputNFC Near-Field CommunicationNR New RadioRAT Radio Access TechnologyRF Radio FrequencyRRC Radio Resource ControlTRP Transmission and Reception PointUE User EquipmentUI User InterfaceWCDMA Wideband Code Division Multiple AccessWiMAX Worldwide Interoperability for Microwave AccessWLAN Wireless Local Area NetworkREFERENCE SIGNS LIST

Claims

CLAIMS:

1. An apparatus, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:- receive a first direct transmission from a wireless device in at least one first downlink transmission time period;- receive in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked;- determine information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device;- determine information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment; and- transmit said information about the second wireless channel to the wireless device.

2. The apparatus according to claim 1, wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to:- receive the first direct transmission in the at least one first downlink transmission time period, and the second direct transmission and the indirect transmission in the at least one second downlink transmission time period, within a channel coherence time of the first wireless channel.

3. The apparatus according to claim 1 or claim 2, wherein the at least one first downlink transmission time period for the first direct transmission and the at least one second downlink transmission time period for the second direct transmission and indirect transmission are configured in relation with a time selectivity of the first wireless channel.

4. The apparatus according to any of the preceding claims, wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to:- receive the first direct transmission in the at least one first downlink transmission time period, and the second direct transmission and indirect transmission in the at least one second downlink transmission time period, within a sampling time of the apparatus.

5. The apparatus according to any of the preceding claims, wherein the first direct transmission and the second direct transmission are beamformed to cover the apparatus and the user equipment.

6. The apparatus according to any of the preceding claims, wherein the apparatus is another user equipment and the wireless device is a wireless network node.

7. The apparatus according to any of the preceding claims, wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to:- receive, from the wireless device, a configuration for receiving transmissions in the at least one first downlink transmission time period and in the at least one second downlink transmission time period.

8. An apparatus, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:- receive a first direct transmission from a wireless device in at least one first uplink transmission time period;- receive in at least one second uplink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked;- determine information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device;- determine information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the apparatus and the user equipment; and- track the user equipment using said information about the second wireless channel.

9. The apparatus according to claim 8, wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to:- receive the first direct transmission in the at least one first uplink transmission time period, and the second direct transmission and indirect transmission in the at least one second uplink transmission time period, within a channel coherence time of the first wireless channel.

10. The apparatus according to claim 8 or claim 9, wherein the at least one first uplink transmission time period for the first direct transmission and the at least one second uplink transmission time period for the second direct transmission and the indirect transmission are configured in relation with a time selectivity of the first channel.

11. The apparatus according to any of claims 8 to 10, wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to:- receive the first direct transmission in the at least one first uplink transmission time period, and the second direct transmission and the indirect transmission in the at least one second uplink transmission time period, within a sampling time of the apparatus.

12. The apparatus according to any of claims 8 to 11, wherein the first direct transmission and the second direct transmission are beamformed to cover the wireless device and the user equipment.

13. The apparatus according to any of claims 8 to 12, wherein the apparatus is a wireless network node and the wireless device is another user equipment.

14. The apparatus according to any of claims 8 to 13, wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to:- transmit, to the wireless device, a configuration for transmitting during the at least one first uplink transmission time period and the at least one second uplink transmission time period.

15. The apparatus according to any of claims 8 to 14, wherein the stored instructions further cause, when executed by the at least one processor, the apparatus at least to:- receive information about a third channel, wherein the third channel is between the wireless device and the user equipment to be tracked; and- determine said information about the second wireless channel based on said information about the third channel.

16. A method, comprising: receiving, by an apparatus, a first direct transmission from a wireless device in at least one first downlink transmission time period; receiving, by the apparatus, in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked; determining, by the apparatus, information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device; determining, by the apparatus, information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment; and transmitting, by the apparatus, said information about the second wireless channel to the wireless device.

17. A method, comprising: receiving, by an apparatus, a first direct transmission from a wireless device in at least one first uplink transmission time period;receiving, by the apparatus, in at least one second uplink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked; determining, by the apparatus, information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device; determining, by the apparatus, information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the apparatus and the user equipment; and tracking, by the apparatus, the user equipment using said information about the second wireless channel.

18. An apparatus, comprising: means for receiving a first direct transmission from a wireless device in at least one first downlink transmission time period; means for receiving in at least one second downlink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked; means for determining information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device; means for determining information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the wireless device and the user equipment; and means for transmitting said information about the second wireless channel to the wireless device.

19. An apparatus, comprising:means for receiving a first direct transmission from a wireless device in at least one first uplink transmission time period; means for receiving in at least one second uplink transmission time period a second direct transmission from the wireless device and an indirect transmission of the second direct transmission of the wireless device via a user equipment to be tracked; means for determining information about a first wireless channel based on the first direct transmission, wherein the first wireless channel is between the apparatus and the wireless device; means for determining information about a second wireless channel based at least on the determined information about the first wireless channel, the second direct transmission and the indirect transmission, wherein the second wireless channel is between the apparatus and the user equipment; and means for tracking the user equipment using said information about the second wireless channel.

20. A non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the method of claim 16 or 17.

21. A computer program comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the method of claim 16 or 17.

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