TECHNICAL FIELD

[0001] This invention relates generally to direct communications between user equipment and, more specifically, relates to discovery procedures for the user equipment to undergo the direct communications.

BACKGROUND

[0002] This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below, after the main part of the detailed description section.

[0003] A set of technologies allows UE to communicate directly from UE to UE, without going through a base station (e.g., an eNB) as an intermediary node. These technologies are referred to by a number of names. For instance, Device to Device (D2D) communications are also known as Proximity Services (ProSe), direct communications, or sidelink operation/communications. For ease of reference, the term direct communications (DCs) will be primarily used herein. One of the most appealing features of direct communications is a UE-to-network relay functionality and some basic functionality was specified in 3GPP LTE Rel-13. As one example, a solution was specified in 3GPP LTE Rel-13, where a UE may act as a ProSe UE-to-network relay to provide connectivity between a further UE and a network by using layer-3 packet forwarding, e.g., see 3GPP TS 23.303. However, efficiency and applicability of an LTE Rel-13 ProSe UE-to-network relay or the solution (thereof) is limited, as selected key drivers for the specification have focused on only public safety usage and not addressed any particular efficiency aspects. Therefore it is very likely that enhancements will be specified in 3GPP Rel-14/15 and subsequent 3GPP releases. Non-3GPP technologies also take advantage of this type of communications already, e.g., WiFi Direct, where Wi-Fi is a technology based on IEEE 802.11 that allows electronic devices to connect to a wireless local area network (WLAN). Efficient UE-to-network relay function is of high importance, especially in the public safety services area as well as for the support of low-power Internet of Things (IoT) and wearables.

[0004] The UE-to-network relaying function is a feature implemented in the UE and the network, which allows a certain UE (called a remote UE) to establish connectivity with the network (e.g., eNB and/or serving gateway) using another UE (called a relay UE) as an intermediate node used to forward the data (e.g., user-plane and control-plane data, including application data) between the remote UE and the network eNB for example. There are various occasions where the relaying functionality is beneficial, such as the following:

[0005] Spectral efficiency in the cell and therefore the network can be increased when the relay UE has better radio conditions than the remote UE;

[0006] The remote UE may be able to use network-provided communications services (e.g., voice, Internet, video, and the like) even when the remote UE is out of network coverage or in poor radio conditions;

[0007] A better QoS can be achieved for the remote UE when the relay UE has better radio conditions than the remote UE;

[0008] Less complex, less costly and smaller form-factor devices as remote UE may be introduced into the network without impacting the efficiency of network resources utilization; and/or

[0009] Power consumption efficiency of remote UEs can be increased.

[0010] Therefore, it is beneficial to improve direct communications. BRIEF SUMMARY

[0011] This section is meant to be exemplary and not meant to be limiting.

[0012] An exemplary method is disclosed, comprising: sending by first user equipment a discovery request comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by a second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by the second user equipment and a wireless communication network; and monitoring by the first user equipment the first wireless resource to determine whether a discovery response is received from the second user equipment.

[0013] An additional example of an embodiment includes a computer program, comprising code for performing the method of the previous paragraph, when the computer program is run on a processor. The computer program according to this paragraph, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

[0014] An example of an apparatus includes one or more processors and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: sending by first user equipment a discovery request comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by a second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by the second user equipment and a wireless communication network; and monitoring by the first user equipment the first wireless resource to determine whether a discovery response is received from the second user equipment.

[0015] In a further example, an apparatus comprises: means for sending by first user equipment a discovery request comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by a second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by the second user equipment and a wireless communication network; and means for monitoring by the first user equipment the first wireless resource to determine whether a discovery response is received from the second user equipment.

[0016] An example of a computer program product includes a computer-readable storage medium bearing computer program code embodied therein for use with a computer. The computer program code includes: code for sending by first user equipment a discovery request comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by a second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by the second user equipment and a wireless communication network; and code for monitoring by the first user equipment the first wireless resource to determine whether a discovery response is received from the second user equipment.

[0017] Another exemplary embodiment is a method, comprising: receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by the second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by a wireless communication network; and sending on the first wireless resource the discovery response from the second user equipment towards the first user equipment.

[0018] A further example of an embodiment includes a computer program, comprising code for performing the method of the previous paragraph, when the computer program is run on a processor. The computer program according to this paragraph, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

[0019] An example of an apparatus includes one or more processors and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by the second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by a wireless communication network; and sending on the first wireless resource the discovery response from the second user equipment towards the first user equipment.

[0020] An example of a computer program product includes a computer-readable storage medium bearing computer program code embodied therein for use with a computer. The computer program code includes: code for receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by the second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by a wireless communication network; and code for sending on the first wireless resource the discovery response from the second user equipment towards the first user equipment.

[0021] In another exemplary embodiment, an apparatus comprises: means for receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by the second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by a wireless communication network; and means for sending on the first wireless resource the discovery response from the second user equipment towards the first user equipment.

[0022] Another exemplary embodiment is a method. The method comprises: sending on a first wireless resource and by a first user equipment a discovery request to a second user equipment, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network, and wherein the second user equipment is to determine the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; monitoring the downlink resource to determine whether a discovery response is received from the second user equipment, and in response to reception of the discovery response, communicating data via direct communications between the first and second user equipment, wherein the data is to be relayed by the second user equipment to a network node of the communication system.

[0023] An additional example of an embodiment includes a computer program, comprising code for performing the method of the previous paragraph, when the computer program is run on a processor. The computer program according to this paragraph, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer. [0024] An example of an apparatus includes one or more processors and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: sending on a first wireless resource and by a first user equipment a discovery request to a second user equipment, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network, and wherein the second user equipment is to determine the second wireless resource based on the pair and use of the first wireless resource to send the discovery request;

monitoring the downlink resource to determine whether a discovery response is received from the second user equipment, and in response to reception of the discovery response, communicating data via direct communications between the first and second user equipment, wherein the data is to be relayed by the second user equipment to a network node of the communication system.

[0025] An example of a computer program product includes a computer-readable storage medium bearing computer program code embodied therein for use with a computer. The computer program code includes: code for sending on a first wireless resource and by a first user equipment a discovery request to a second user equipment, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network, and wherein the second user equipment is to determine the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; code for monitoring the downlink resource to determine whether a discovery response is received from the second user equipment, and in response to reception of the discovery response, communicating data via direct communications between the first and second user equipment, wherein the data is to be relayed by the second user equipment to a network node of the communication system.

[0026] An additional exemplary embodiment is an apparatus, comprising: means for sending on a first wireless resource and by a first user equipment a discovery request to a second user equipment, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network, and wherein the second user equipment is to determine the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; means for monitoring the downlink resource to determine whether a discovery response is received from the second user equipment, and in response to reception of the discovery response, communicating data via direct communications between the first and second user equipment, wherein the data is to be relayed by the second user equipment to a network node of the communication system.

[0027] In an additional exemplary embodiment, a method is disclosed. The method comprises: receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and received on a first wireless resource, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network; determining by the second user equipment the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; sending on the determined second resource the discovery response from the second user equipment toward the first user equipment; communicating data via direct communications on an established direct communications connection between the first and second user equipment; and relaying the communicated data from the second user equipment to a network node of the communication system.

[0028] An additional example of an embodiment includes a computer program, comprising code for performing the method of the previous paragraph, when the computer program is run on a processor. The computer program according to this paragraph, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

[0029] An example of an apparatus includes one or more processors and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and received on a first wireless resource, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network; determining by the second user equipment the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; sending on the determined second resource the discovery response from the second user equipment toward the first user equipment; communicating data via direct communications on an established direct communications connection between the first and second user equipment; and relaying the communicated data from the second user equipment to a network node of the communication system.

[0030] An example of a computer program product includes a computer-readable storage medium bearing computer program code embodied therein for use with a computer. The computer program code includes: code for receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and received on a first wireless resource, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network; code for determining by the second user equipment the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; code for sending on the determined second resource the discovery response from the second user equipment toward the first user equipment; code for communicating data via direct communications on an established direct communications connection between the first and second user equipment; and code for relaying the communicated data from the second user equipment to a network node of the communication system.

[0031] A further exemplary embodiment is an apparatus, comprising: means for receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and received on a first wireless resource, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network; means for determining by the second user equipment the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; means for sending on the determined second resource the discovery response from the second user equipment toward the first user equipment; means for communicating data via direct communications on an established direct communications connection between the first and second user equipment; and means for relaying the communicated data from the second user equipment to a network node of the communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the attached Drawing Figures:

[0033] FIG. 1 is a block diagram of one possible and non-limiting exemplary system in which the exemplary embodiments may be practiced;

[0034] FIG. 2 illustrates an overall concept of Model B discovery in 3GPP, and is a modified version of "Figure 5.3.7.1-2: Public safety direct discovery with Model B" from 3GPP TS 23.303 (e.g., see 3GPP TS 23.303 V14.0.0 (2016-09));

[0035] FIG. 3, which is divided into FIGS. 3A and 3B, is a logic flow diagram for relay discovery procedures for direct communications, and illustrates the operation of an exemplary method or methods, a result of execution of computer program instructions embodied on a computer readable memory, functions performed by logic implemented in hardware, and/or interconnected means for performing functions in accordance with exemplary embodiments;

[0036] FIG. 4 is an exemplary signaling diagram illustrating one possible sequence of operations for relay discovery;

[0037] FIG. 5 is a logic flow diagram for implicit indication of the resource allocation relay allocation and use thereof for a discovery procedure for direct communications, and illustrates the operation of an exemplary method or methods, a result of execution of computer program instructions embodied on a computer readable memory, functions performed by logic implemented in hardware, and/or interconnected means for performing functions in accordance with exemplary embodiments. DETAILED DESCRIPTION OF THE DRAWINGS

[0038] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described in this Detailed Description are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims.

[0039] The exemplary embodiments herein describe techniques for and additional information about relay discovery procedures for direct communications that improve power consumption. Additional description of these techniques is presented after a system into which the exemplary embodiments may be used is described.

[0040] Turning to FIG. 1, this figure shows a block diagram of one possible and non-limiting exemplary system in which the exemplary embodiments may be practiced. In FIG. 1, a user equipment (UE) 110 and N UEs 115 are in wireless communication with a wireless communication network 100. A UE 110 or 115 is a wireless, typically mobile device that can access a wireless network. Each UE 110 or 115 communicates with the wireless communication network 100 via a base station shown here as eNB 170, through a corresponding wireless link 111 or 113-1 through 113- N. Additionally, the UE 110 communicates via direct communications with UEs 115-1 through 115- N via corresponding DC wireless links 112-1 through 112-N. The UE 110 will also be referred to herein as a remote UE or discoverer UE, while the UEs 115 will also be referred to as relay UEs or discoveree UEs.

[0041] Concerning "cells", a cell makes up part of an eNB. That is, there can be multiple cells per eNB. For instance, there could be three cells for a single eNB carrier frequency and associated bandwidth, each cell covering one-third of a 360 degree area so that the single eNB's coverage area covers an approximate oval or circle. Furthermore, each cell can correspond to a single carrier and an eNB may use multiple carriers. So if there are three 120 degree cells per carrier and two carriers, then the eNB has a total of 6 cells. It should be clear that a reference to a cell performing a function means the eNB performs the function.

[0042] The communication system illustrated in FIG. 1 is an LTE system, but this is merely exemplary. While the examples herein may be targeted for 3GPP Rel-14 and beyond systems (e.g., 5G), they may also be applicable to other radio technologies like WLAN. In WLAN, the base station is typically called an access point (AP), and UEs are commonly referred to using other names, such as mobile stations. Furthermore, combinations of these may be used, such as having the LTE system configure the UEs 110 and 115 for direct communications, but the direct communications might be performed by WLAN or other technologies. Additionally, the UEs 110 and 115 are all shown being connected to or attached to one eNB 170, but the UEs may be connected to or attached to different eNBs 170 (e.g., even as part of different PLMNs).

[0043] It is assumed that the UEs 110 and 115 are each relatively similar, so the possible internal configuration of one UE (UE 110) is described and the other UEs are considered to be the same. The UE 110 includes one or more processors 120, one or more memories 125, and one or more transceivers 130 interconnected through one or more buses 127. Each of the one or more transceivers 130 includes a receiver, Rx, 132 and a transmitter, Tx, 133. The one or more buses 127 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, and the like. The one or more transceivers 130 are connected to one or more antennas 128. The one or more memories 125 include computer program code 123. The UE 110 includes a DC (direct communications) module 140, comprising one of or both parts 140-1 and/or 140-2, which may be implemented in a number of ways. The DC module 140 may be implemented in hardware as DC module 140-1, such as being implemented as part of the one or more processors 120. The DC module 140-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the DC module 140 may be implemented as DC module 140-2, which is implemented as computer program code 123 and is executed by the one or more processors 120. For instance, the one or more memories 125 and the computer program code 123 may be configured to, with the one or more processors 120, cause the user equipment 110 to perform one or more of the operations as described herein.

[0044] The eNB (evolved NodeB) 170 is a network node, typically a base station (e.g., for

LTE, long term evolution), that provides access by wireless devices such as the UE 110 to the wireless communication network 100. The eNB 170 includes one or more processors 152, one or more memories 155, one or more network interfaces (N/W I/F(s)) 161, and one or more transceivers 160 interconnected through one or more buses 157. Each of the one or more transceivers 160 includes a receiver, Rx, 162 and a transmitter, Tx, 163. The one or more transceivers 160 are connected to one or more antennas 158. The one or more memories 155 include computer program code 153. The eNB 170 includes a DC module 150, comprising one of or both parts 150-1 and/or 150-2, which may be implemented in a number of ways. The DC module 150 may be implemented in hardware as DC module 150-1, such as being implemented as part of the one or more processors 152. The DC module 150-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the DC module 150 may be implemented as DC module 150-2, which is implemented as computer program code 153 and is executed by the one or more processors 152. For instance, the one or more memories 155 and the computer program code 153 are configured to, with the one or more processors 152, cause the eNB 170 to perform one or more of the operations as described herein. The one or more network interfaces 161 communicate over a network such as via the links 176 and 131. Two or more eNBs 170 communicate using, e.g., link 176. The link 176 may be wired or wireless or both and may implement, e.g., an X2 interface.

[0045] The one or more buses 157 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, wireless channels, and the like. For example, the one or more transceivers 160 may be implemented as a remote radio head (RRH) 195, with the other elements of the eNB 170 being physically in a different location from the RRH, and the one or more buses 157 could be implemented in part as fiber optic cable to connect the other elements of the eNB 170 to the RRH 195. In this case, the RRH 195 is a network node that interfaces with the UE 110 (and also with part of the eNB 170).

[0046] The wireless communication network 100 may include a network control element (NCE) 190 that may include MME (Mobility Management Entity)/SGW (Serving Gateway) functionality, and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the Internet). The eNB 170 is coupled via a link 131 to the NCE 190. The link 131 may be implemented as, e.g., an SI interface. The NCE 190 includes one or more processors 175, one or more memories 171, and one or more network interfaces (NAV I/F(s)) 180, interconnected through one or more buses 185. The one or more memories 171 include computer program code 173. The one or more memories 171 and the computer program code 173 are configured to, with the one or more processors 175, cause the NCE 190 to perform one or more operations.

[0047] The computer readable memories 125, 155, and 171 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The computer readable memories 125, 155, and 171 may be means for performing storage functions. The processors 120, 152, and 175 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples. The processors 120, 152, and 175 may be means for performing functions, such as controlling the UE 110, eNB 170, and other functions as described herein.

[0048] In general, the various embodiments of the user equipment 110 can include, but are not limited to, cellular telephones such as smart phones, tablets, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, tablets with wireless communication capabilities, as well as portable units or terminals that incorporate combinations of such functions.

[0049] Having thus introduced one suitable but non-limiting technical context for the practice of the exemplary embodiments of this invention, the exemplary embodiments will now be described with greater specificity.

[0050] The exemplary embodiments herein propose new mechanisms for relay discovery procedure, which are required before data forwarding from a remote UE to a network via a relay UE/node can take place, and the new mechanisms would be implemented by UEs supporting these functions and have some impact on eNB implementation.

[0051] As mentioned above, one of the potential benefits of direct communications, which may be provided by UE-to-network relaying functionality, is a decrease in power consumption of the remote UE. Optimizations in terms of power consumption are beneficial for wearable devices like smartwatches, fit-bands, heart monitors, body sensors, eye-glasses, and the like. These devices may be characterized by small form-factor, but at the same time are expected to provide long operation without the need to recharge their battery. Similar requirements concern devices used for Machine Type Communications (MTC) or Internet of Things (IoT) communications, including those devices associated with a person in a more extended personal area or space such as devices mounted on equipment or a vehicle or a home. Such devices could be, for instance, sensors or devices of smart homes/cars for remote monitoring or controlling applications (e.g., security and insurance related services, food/drink supply related services, nursing related services, etc.)

[0052] On the other hand, the current UE-to-network relaying framework in 3GPP was created especially for public safety devices, for which high battery consumption is not a primary issue, and currently existing procedures do not take into account battery lifetime constraints of wearable or MTC/IoT devices. In particular, the relay discovery procedure, which is a prerequisite for direct link establishment between the relay UE 115 and remote UE 110 and for relaying or relayed communications or communication between the remote UE and the (serving) network (e.g., eNB or a network server) via the relay UE is inefficient in terms of the remote UE' s power consumption. The exemplary embodiments herein address this particular aspect of UE-to-network relaying feature.

[0053] Currently in order to perform relay discovery, the remote UE 110 can use either

Model A or Model B discovery as described in "3GPP TS 23.303, Proximity-based services (ProSe); Stage 2". Each of these models requires a remote UE 110 to listen to a sidelink discovery channel and detect Discovery Announcement or Discovery Response messages in the discovery resource pool (e.g., meaning time/frequency resources dedicated to sidelink discovery), which is either pre- configured on the UE 110 or provided to the UE 110 from the network (e.g., the eNB 170) by the means of broadcast or dedicated signaling.

[0054] FIG. 2 illustrates an overall concept of Model B discovery in 3GPP, and is a modified version of "Figure 5.3.7.1-2: Public safety direct discovery with Model B" from 3GPP TS 23.303 (e.g., see 3GPP TS 23.303 V14.0.0 (2016-09)). In this example, the UE-1 is a remote UE 110 and is a discoverer, while UE-2 through UE-5 are UEs 115-1 through 115-4, respectively, and are discoverees. The discoverer UE 110 sends Solicitation messages 210-1 through 210-4 to the discoveree UEs 115-1 through 115-4, and receives Response messages 220-1 and 220-2 from the discoveree UEs 115-1 and 115-2, respectively. These messages 210 and 220 can be used in the examples herein, with modifications that are described below.

[0055] The discovery resource pool is dimensioned by the eNB 170 depending on the number of expected discovery messages, which are to be sent by the D2D capable devices. With more and more wearable and IoT devices emerging in the networks, and with the introduction of a UE-to- network relay function for commercial use cases, this number is expected to be very high. This in turn leads to the need to provision a large discovery resource pool used for reception, which needs to be monitored by the remote UE 110 to identify the desired discovery messages from a potential relay UE 115 candidate. This in turn requires the remote UE's receiver to be active for a significant amount of time (e.g., rather frequent in the long run) and to scan a potentially broad resource pool to find a suitable or targeted relay UE, which leads to a high battery consumption of such a remote UE 110.

[0056] The exemplary embodiments aim at providing an enhanced relay discovery procedure allowing remote UEs 110 (e.g., wearables, IoT devices) to reduce their power consumption as compared to the state of the art solutions. The idea for an exemplary embodiment is to have the remote UE 110 initiate the relay request, preferably to a pre-determined target relay UE 115, as in Model B but, further to the current Model B, the remote UE 110 allocates resources on which the remote UE 110 expects to monitor for a possible response from the targeted relay UE 115. That is, the sender of a discovery message may allocate a resource on which the targeted receiver of the discovery message is expected to respond on (the allocation may also be implicit as explained below). This eliminates the need for scanning, receiving and filtering all possible discovery messages, which in turn reduces the power consumption for the remote UE notably. It is noted this case is optimized for the remote UE. The relay UE, as in the current Rel-13 or Rel-14, is to monitor the whole resource pool as configured by the network (e.g., the eNB via SIB or with once-off pre-configuration for some examples) and receipt request(s) sent on any resource instances of the configured resource pool.

[0057] An example of one possible proposed procedure is as follows. This procedure is described in reference to FIG. 3, which is divided into FIGS. 3A and 3B. This figure is a logic flow diagram for relay discovery procedures for direct communications, and illustrates the operation of an exemplary method or methods, a result of execution of computer program instructions embodied on a computer readable memory, functions performed by logic implemented in hardware, and/or interconnected means for performing functions in accordance with exemplary embodiments. For instance, the DC modules 140 and/or 150 may include multiples ones of the blocks in FIG. 3, where each included block is an interconnected means for performing the function in the block. The blocks in FIG. 3 are assumed to be performed by the UE 110, e.g., under control of the DC module 140 at least in part, the UEs 115, e.g., under control of the DC module 140 at least in part, and the eNB 170, e.g., under control of the DC module 150 at least in part.

[0058] In addition to the blocks illustrated in FIG. 3, this exemplary procedure is divided into six broad steps, marked as 1 through 6 below.

[0059] Step 1. The network (e.g., the eNB 170) configures UEs 110/115 with the discovery resource pool to be used for transmission (e.g., a transmission discovery resource pool) and the discovery resource pool to be used for reception (e.g., a reception discovery resource pool), where the UEs should transmit and monitor (respectively) for relay related direct discovery messages. See block 305. It is noted that, for a remote UE without coverage of an eNB, Rel-13 and Rel-14 rely on pre- configurations (e.g., preconfigured resource pools as part of subscription profile or some once-off pre- configuration) for out-of-coverage operation. That is, currently out-of-coverage UEs are preconfigured with a resource pool. This can mean that configuration (e.g., in the form of a file) is uploaded on the UE or in the SIM card, although other techniques are also possible. It should be further noted that such pre-configuration may be used for UEs for other purposes other than out-of- coverage operations.

[0060] Step 2. A UE, acting as a remote UE (e.g., which may be configured by the network to act as such), sends a relay discovery message (e.g., a modified version of the solicitation message 210 of FIG. 2) including additional information (see block 315), which in particular can comprise one or more of a remote UE ID, a service ID and a relay UE ID if known. The service ID refers to, e.g., 3GPP TS 23.303, Relay Service Code, which is information about connectivity that the discoverer UE is interested in. The Relay Service Codes are configured in the remote UEs interested in related connectivity services. Service codes are likely to be used where there is no specific relay UEs paired with remote UEs, so the remote UE searches for any relay UE that might provide the remote UE with specific connectivity service. Other options may be also Group ID (e.g., a UE searches for any relay UE belonging to some group of UEs, e.g., firefighter' s Public Safety UEs). The relay UE ID is an ID corresponding to a relay UE 115 that is already known to the remote UE 110, and typically any of the identifiers mentioned in this step should be known to the remote UE 110 beforehand. This knowledge can be realized via pre-configuration in a similar way as that of pre-configured resource pools for out- of-coverage operation. Additionally, and prior to sending the message, the Remote UE performs resource selection (see block 310) from the network configured resource pool, e.g., according to the rules specified for the technology in use or by narrowing down the configured resource pool to a subset of resources from the ones configured by the network. The parameters, which uniquely identify the chosen resources within the network configured resource pool (e.g., indices, pointers to time/frequency, frame and/or sub-frame number, subcarrier number, and the like) are also attached to the discovery message, e.g., a modified version of the Solicitation message 210 of FIG. 2, to indicate the resources in which the remote UE 110 will monitor for the response from the relay UE 115. Additionally based on UE or network configuration or based on other factors like, e.g., cell load, interference, resources utilization and the like, the remote UE 110 can provide additional information about the additional time periods the remote UE 110 is going to monitor for the response in case during the original timeslot a collision occurs or the relay UE 115 will not be able to send the response message for another reason.

[0061] Step 3. A UE, which is configured by the network to act as a Relay UE monitors (block 320) the reception discovery resource pool for the relay discovery messages transmitted by remote UEs 110. If a message is not detected (block 325 = No), the relay UE 115 continues to monitor the reception discovery resource pool in block 320. When the relay UE 115 detects the message (block 325 = Yes) from the remote UE 110 for which the relay UE 115 is configured to serve (e.g., based on at least one of the remote UE ID, relay UE ID, service ID, group ID, or a combination thereof, included in the received discovery message), the relay UE 115 prepares (block 330) a discovery response message including additional information required for the remote UE 110 to establish a connection with the relay UE 115 and subsequently with the network. The additional information could be, for instance, information about the relay UE 115, provided services, configuration details, network information, and the like. In particular, the message should contain the remote UE ID for which the response is prepared and/or service ID, for which the response message is intended. The relay UE reads (block 335) also the information about the exact resources where the relay UE 115 should transmit the response message, which was previously chosen and attached to the relay discovery message sent by the Remote UE as described in step 2 of the procedure. Instead of choosing the discovery transmission resources randomly or according to other rules specified for the used technology, the relay UE 115 uses the resources indicated in the relay discovery message and transmits (see block 340) its discovery response message (e.g., a modified version of the Response message 220 of FIG. 2) on these resources.

[0062] Step 4. The remote UE 110, after sending (see block 315) the discovery message, monitors (block 350) for the response discovery message sent by the relay UE candidate on the resources the remote UE candidate previously chose and indicated in the relay discovery message instead of monitoring the whole reception discovery resource pool. This monitoring may be performed as follows.

[0063] Step 4a. If the remote UE 110 receives the response discovery message (block 355 = Yes), the remote UE 110 proceeds to step 5 of the procedure (see block 385); otherwise (block 355 = No), the remote UE proceeds to block 360.

[0064] Step 4b. If the remote UE 110 does not receive the response in the first expected time period (e.g., the first time period is over, block 360 = Yes), the remote UE 110 can optionally monitor (block 365) for the response in the subsequent time periods if provided in the relay discovery message or configured by the network or according to specified behavior. Concerning these time periods, the time period here refers to the reoccurring or recurrence of the targeted resource(s) within a discovery time period. For example, if the resource pool is specified for a recurrence of 40ms and the discovery time period is configured as 200ms, then there are five expected time periods. Is it also appropriate to consider that the first expected time period could refer to a first selected resource for monitoring, and subsequent time periods could refer to a second selected resource for monitoring. As another example, the first and the subsequent time periods may use different resources for discovery response message transmission. However, in order to save the signaling overhead for indicating the response message resources by the remote UE, the resource pattern may be pre-defined so that a UE can derive the resource in the subsequent time periods based on the resource used in the first time period.

Another example is only one indicated resource will be used in the first time period and a gradually increased sub-set of the resource pool can be used in the subsequent time periods so that the remote UE only monitors the dedicated resource for the first time period and monitors more resources in the subsequent time periods for more robustness.

[0065] If the first time period is not over (block 360 = No), the flow proceeds to block 350 where the remote UE 110 continues to monitor the resources the remote UE candidate previously chose. It is noted that block 375 is an optional fallback option and there is no optimization when block 375 is applied. The optimization in the previous steps is due to the limited amount of resource instances (e.g., one or several) out of the preconfigured much larger resource pool the remote UE needs to monitor. For the optional monitoring in block 375, if the remote UE 110 receives (block 370 = Yes) the response discovery message during these occasions, the remote UE 110 proceeds to step 5 (see block 385 also).

[0066] Step 4c. If the remote UE 110 does not receive the response message (block 370 = No, and as Alternative 1), the remote UE 110 assumes there is no suitable Relay UE candidate in its proximity and based on its configuration, implementation or preferred action it may choose to either transit into inactive mode or attempt to establish connection directly with the network and the procedure ends (block 397).

[0067] Step 4d. Alternative behavior (illustrated as block 370 = No, and as Alternative 2) may be specified for the out of coverage remote UEs 110, which do not know the network configuration, which may, e.g., disallow discovery resource pre-selection. In that case, instead of transiting into inactive mode, a UE may attempt to monitor (block 375) for the discovery response message in the whole resource pool, which is pre-configured on the UE or which was configured on the remote UE 110 by the network while the remote UE 110 was in coverage of the network. If the response would not be received in a specified time the UE could transit into inactive mode and repeat the procedure later on. This is illustrated by the remote UE not receiving the response (block 380 = NO) and ending this instance of the process in block 397. Otherwise (block 380 = Yes), the response is received, and the remote UE 110 proceeds to step 5 (also see block 385).

[0068] Additional alternative behaviors are also possible, such as the following:

[0069] - The UE repeats the procedure and chooses another set of resources at block

310;

[0070] - The UE repeats the discovery procedure at block 310 but does not indicate the particular resources and listens to the whole resource pool; and/or

[0071] - The UE establishes direct connection with the network if possible.

[0072] Decision on the behavior could, e.g., depend on whether collision was detected (if collision was detected, it means that there could be a relay UE which was trying to answer; if collision was not detected then probably there is no eligible relay in vicinity. Monitoring the whole resource pool when no message is detected in the indicated resources might not make sense and could lead to increase of power consumption instead of decreased power consumption.

[0073] Step 5. The remote UE 110 uses (block 385) the information provided inside the response message to establish a direct and joint communication connection (e.g., over a link 112) with the relay UE 115, which provided the response. Additionally, subsequently the connections between the network and remote UE 110 as well as between the network and relay UE 115 are established, e.g., over corresponding links 111. See block 390. [0074] Step 6. Data relaying between Remote UE and the network can start. See block 395. In particular, data is relayed between the remote UE and the network using the established connections.

[0075] Turning to FIG. 4, this figure is an exemplary signaling diagram illustrating one possible sequence of operations for relay discovery. In this example, there is one relay UE 115 and Y remote UEs 110-1 through 100-Y. It is noted that some of the material described in reference to FIG. 4 is also described elsewhere in this document, but FIG. 4 provides a succinct overview of the relay discovery process, and thus material may be repeated here for clarity.

[0076] In step 4-1, the network (the eNB 170 in this example) configures (e.g., using one or more System Information Blocks SIBs) UEs (a relay UE 115, Y remote UEs 110-1 through 110- Y) within a cell with the discovery resource pool for transmission of discovery messages (UL, Tx (discovery) resource pool) and reception of discovery messages (DL, Rx (discovery) resource pool), on which the relay UE 110 should monitor for relay-related direct discovery requests and transmit responses. This is illustrated using a configuration (Config) message with the information of the resource pool for discovery procedure ("resource pool for Discov Proc").

[0077] It is helpful to consider the following clarifications regarding UL and DL in the context of direct communications. An UL resource or DL resource for direct communications such as D2D is referred to as a resource used for a given UE involved in a D2D communication to transmit or receive. These resources are from the corresponding resource pool configured on the UE. In this regard, an UL resource for a Tx UE is considered as a DL resource for an Rx UE in D2D. In Rel-12 through Rel-14, the resource pool for D2D is actually a part of the UL carrier' s resources.

Furthermore, all messages (both Discovery Requests and Discovery Responses) will be sent in a Tx resource pool. Moreover, all messages will be received in an Rx resource pool. This in fact means that Tx resource pool is a subset of Rx resource pool. It should be further noted that a network has a flexibility of configuring different Tx resource pools and different Rx resource pools for different

UEs. In particular, a network could configure different a Tx resource pool and Rx resource pool to be used by the relay UE and a different Tx resource pool and Rx resource pool to be used by the remote UE. As long as the Tx resource pool used by relay UE is a subset of Rx resource pool used by remote UE and vice versa, a relay discovery procedure can be successful.

[0078] Depending on terminology and implementation, there may be no such concept as a

Discovery Request pool and a Discovery Response pool. Instead, there is a discovery transmission resource pool and a discovery reception resource pool. If a UE wants to transmit any discovery message (no matter whether this is Request or Response), the UE uses the transmission pool, and if the UE is monitoring for any discovery message (no matter whether it is relay monitoring for discovery request or remote UE monitoring for Discovery response), the UE uses the discovery reception pool. It can be imagined that, to limit the resources to be monitored by remote UEs, a network could configure separate resource pools for transmission/reception for relay UE and remote UE, resulting in four logical pools being configured:

[0079] 1. A Tx pool for the relay UE (first pool), which would in fact equal to or be a subset of an Rx pool for the remote UE (second pool); and

[0080] 2. A Tx pool for the remote UE (third pool), which would in fact equal to or be a subset of an Rx pool for the relay UE (fourth pool).

[0081] In step 4-2, in response to receiving the configuration messages, this enables the remote UE 110-1 to initiate a relay discovery procedure. The remote UE 110-1 selects at least one first resource to monitor and receive an expected response for the discovery (Disco v) procedure from an Rx discovery resource pool and selects at least one second resource for transmitting the discovery request from Tx discovery resource pool to start to search for a relay UE in its proximity (see step 4-3, Discov Req) in order to send the user data via the relay UE (which occurs in steps 4-7, via an established Connection, and 4-8).

[0082] In step 4-3, a discovery request (Discov Req) is sent on the second (e.g., UL) resource of the discovery resource pool for transmission into the area around the remote UE 110-1. The remote UE 110-1 then monitors the at least one first (e.g., DL) resource.

[0083] The at least one first (e.g., DL) resource information 410 may be embodied as an IE added to the Discovery Request message, and this IE can indicate Discovery Response message resources in multiple ways:

[0084] 1) a specific resource index;

[0085] 2) a sub-pool of the resource pool (e.g., when the remote UE expects the response to come from more than one relay UE);

[0086] 3) a set of resource indices or a set of resource sub-pools (e.g., to decrease the probability of collisions).

[0087] These are merely exemplary and it may be possible to use more than one of these. As an example, in the choices (2) and (3), it is not a single resource, but a set of resources that are indicated. It is possible, therefore, that a remote UE 110 chooses as a first wireless resource a set of resource indices (e.g., resource X, resource Y, resource Z) and may also provide a time period length, e.g., T=20ms (or time period may be configured by the network). In the first time period starting at TO, the remote UE 110 monitors resource X. If no response is received, in the second time period starting at T0+20ms the remote UE monitors resource Y. If no response is received, in the third time period starting at T0+40ms, the remote UE monitors resource Z.

[0088] It is further noted that in step 4-3, the remote UE 110 indicates the first resource to be used for Discovery Response in the IE. Additionally, the remote UE 110 can amend the Discovery Request (Discov Req) with the information about the number of repetitions the remote UE 110 is going to listen to. The repetitions may be indicated in, e.g., subsequent discovery periods or be indicated implicitly (e.g., using a specific resource index) or the remote UE 110 could indicate the time periods in which the remote UE is going to be actively monitoring for the response(s).

[0089] In step 4-4, a relay UE 115 monitoring the discovery resource pool detects the Discov

Req message with its indication of the at least one first (e.g., DL) resource of the discovery resource pool. The relay UE 115 evaluates the request, assigns resources to establish a connection, and determines further information to send to the remote UE.

[0090] In step 4-5, the relay UE 115 sends the response 420 ("Discov Rsp" message 420, where Discov is discovery and Rsp is response) on one of the received at least one first resource (e.g., indicated DL resource as seen by the remote UE). In step 4-5, the relay UE 115 uses a first resource of the at least one resource indicated in the received Discov Req. If the relay UE 115 does not receive a connection establishment request before the time for repetition comes, the relay UE 115 may repeat its transmission using repetition rules. Specifically, the general rule is that if a connection establishment request is not received by relay UE after sending first (or second or third or more)

Discovery Response, the relay UE chooses the subsequent resources for sending subsequent discovery responses depending on the implementation choice from the ones mentioned herein in such a way that a remote UE should monitor these resources according to the techniques also presented herein. As examples, if the relay UE does not receive a response then the relay UE may repeat the discovery response message (sends it again) on the next resource, which depending on the implementation may be, e.g., the same resource but with a given time offset, another resource indicated by the resource index, another resource in the broader resource sub-pool, and the like. The response can be sent either when the time determined by the timing offset comes or when the time to send the resource indicated by the resource index comes or when some specified timer expires.

[0091] In step 4-6, the remote UE 110-1 monitors the limited set of resources as indicated in step 4-3 and detects the Discov Rsp (discovery response) message with the parameters to proceed with the establishment of a connection between the remote UE 110-1 and the relay UE 115 for user data communication. Resources used for D2D communications after the discovery phase may be from other configured resource pools, and protocols used for D2D communications may be different from those used for discovery.

[0092] In step 4-7, the remote UE 110-1 sends the data towards the network, and this may involve two-way communications between the relay UE 115 and the remote UE 110-1, e.g., over a direct and joint communication connection. It is noted if the relay UE does not detect a connection with associated parameters as in step 4-7, the relay UE assumes the discovery response did not arrive at the remote UE and should be repeated in the further time periods/resources, e.g., as described herein.

[0093] In step 4-8, the relay UE 115 forwards the user data towards the base station and (e.g., the base station forwards the data) further onwards toward the "core" network (e.g., the NCE 190).

[0094] One exemplary advantage of the described procedures over the existing solutions is that the remote UE 110 is not required to monitor a broad resource pool in order to identify the response message from the relay UE 115. That is, the remote UE 110 monitors a smaller resource pool. This reduces the activity time, processing time and complexity of the remote UE 110, which in consequence reduces its power consumption.

[0095] The exemplary embodiments may be targeted for LTE technology and a probable implementation for the cases described above would be based on Model B discovery as described in 3GPP TS 23.303 and in reference to FIG. 2.

[0096] Although relaying functionality was originally specified by 3GPP for public safety use only, this functionality is now studied in Rel-14 for commercial use case as well and specification changes are expected to account for other use cases as well, such as those IoT and wearables use cases mentioned above in addition to public safety. At the same time, it is expected that general rules (e.g., for those of the current Rel-13 and Rel-14 ProSe D2D) will be reused while the focus will be on enhancing power efficiency of the remote UEs 110. The proposals herein have the advantage of reusing the basic framework of discovery procedure and introduce enhancements on Access

Stratum/radio layer to improve and possibly optimize the UE's power consumption. Therefore an aspect of the invention with respect to the procedure above concerns the way the relay UE 115 chooses the resources to provide the response messages depicted in 2a (220-1) and 2b (220-2) in FIG. 2. The eNB 170 can configure the relay UE 115 for discovery message transmissions using two modes: eNB scheduled or UE selected. The exemplary embodiments herein address the situation when the UE selected mode is configured, which is a probable case due to much lower complexity of that scheme compared to the other one (i.e., the eNB scheduled). One difference compared to current solutions is that it would not be the relay UE 115, but the remote UE 110 that performs the resource selection for the message, which is to be sent by the relay UE 115. The selection should account for the time period, which is required to send the original discovery message and process the message inside the relay UE 115.

[0097] There may be some further options on how the resources are chosen based on the UE and network configuration as well as the contents of the discovery message. These options are as follows and can used singularly or in combination (unless the combination is prohibited by the operation of the options). [0098] Option 1. In case the remote UE 110 is configured to cooperate with a relay UE 115 identified by a specific relay UE ID and the discovery message (e.g., the solicitation message 210 in FIG. 2) includes this relay UE ID, then the exact set of resources could be chosen according, e.g., to the currently standardized mechanisms, i.e., a specific resource index would be provided to the relay UE 115.

[0099] Option 2. In case the remote UE 110 is configured to cooperate with multiple relay UEs 115, which provide a specific service identified, e.g., by the Relay Service Code, or which belong to a specific group of UEs identified, e.g. by the same Group ID, the UE would not provide a specific resource index, but instead would provide a resource pool, which is contained in the resource pool configured by the network, but is narrower than this resource pool (i.e., a subset of one or more resource instances of the network configured resource pool) and thus still allows the remote UE 110 to limit its monitoring activity and preserve battery life. At the same time, this allows for a situation when multiple relay UEs 115 supporting the service identified by the Relay Service Code included in the discovery message decide to send the response. In case a single resource is indicated, this would lead to collision, while the narrower resource pool allows for random choice of exact resource and decreases collision probability significantly.

[00100] Option 3. In both cases the collisions might still occur, so in addition the remote UE 110 can indicate the number of repetitions the remote UE 110 is going to listen to. This can apply to the methods described in both Options 1 and 2 above. The repetitions may occur, e.g., in subsequent discovery periods or be indicated implicitly (e.g., using a specific resource index) or the UE could indicate the time periods in which the UE is going to be actively monitoring for the response(s) or the discovery periods may occur using a specified pattern. For instance, the number of recurrences of the targeted resource to be monitored by the remote UE might be five within a 200ms discovery period. The remote UE may choose to monitor every second recurrence or in a predefined but randomized pattern (e.g., 1, 2, 5) over one or multiple discovery periods.

[00101] In a further embodiment, an alternative to using explicit indication of the resource allocation from the sending side in the above examples is to have implicit indication. This alternative may be realized by having the network configure at least two discovery resource pools: one (e.g., Pool_W) is used for the remote UE 110 and another one (e.g., Pool_R) is used for the relay UE 115. Each of the resources in Pool_W and Pool_R are paired beforehand. However, Pool_W and Pool_R may also be considered as parts of the same resource pool, in which the resource instances are given in pairs, e.g., possibly with a certain time offset. Thus, based on the resource on which the wearable (remote UE) sends the discovery request, a relay UE 115 can derive the corresponding resource in Pool_R to be used for a discovery response using the corresponding pair. In this way, the wearable can also derive the same resource to listen to/receive the discovery response. This option in one way saves the signaling overhead without explicit indication of pre-selected resources and on the other hand does not require any change of current Rel-12/13 discovery mechanism (i.e., transparent MAC for discovery without adding any access stratum (AS) level information in the discovery message). Regarding the time offset, a simple usage for this would be, e.g., the remote UE sends the discovery request message on resource j, then the relay UE will send the discovery response message on resource j too but shifted with the "time offset" in the time domain.

[00102] Note that for explicit resource indication, a UE needs to either have such resource information indicated from a higher layer to the MAC layer or change the current Rel-12/13 discovery mechanism to include AS information in the discovery message. That is, the AS information could include resource indication for discovery messages. In this regard, for the UE to be able to distinguish between Rel-12/13 discovery messages and the enhanced discovery messages for wearables including AS information, either the enhanced discovery messages are transmitted in exclusive resource pool from that of Rel-12/13 discovery messages or otherwise using different physical formats or considering relay discovery application for wearables is a part of AS.

[00103] Turning to FIG. 5, a logic flow diagram is shown for implicit indication of the resource allocation relay allocation and use thereof for a discovery procedure for direct

communications. This figure also illustrates the operation of an exemplary method or methods, a result of execution of computer program instructions embodied on a computer readable memory, functions performed by logic implemented in hardware, and/or interconnected means for performing functions in accordance with exemplary embodiments. For instance, the DC modules 140 and or 150 may include one or more of the blocks in FIG. 5, where each included block is an interconnected means for performing the function in the block. The blocks in FIG. 5 are assumed to be performed by the UE 110, e.g., under control of the DC module 140 at least in part, the UEs 115, e.g., under control of the DC module 140 at least in part, and the eNB 170, e.g., under control of the DC module 150 at least in part.

[00104] In block 510, the network (e.g., the eNB 170) configures at least two discovery resource pools: one (e.g., Pool_W) is used for the remote UE and another one (e.g., Pool_R) is used for the relay UE. The resource instances are given in pairs. In block 515, the remote UE 110 selects one of the pairs. The remote UE 110, in block 520, sends a discovery request on a wireless (e.g., UL) resource from the selected pair.

[00105] In block 525, the relay UE 115 receives the discovery request on the wireless (e.g., UL) resource from the selected pair. The relay UE, in block 530, determines a wireless (e.g., DL) resource from the selected pair to use to send the discovery response, based on the wireless resource used for discovery request. That is, based on the wireless (e.g., UL) resource, the relay UE 115 then determines the pair that was previously selected by the remote UE 110 and also the wireless (e.g., DL) resource to use from that pair for sending the discovery response. In block 540, the relay UE 115 sends the discovery response on the wireless (e.g., DL) resource determined from the selected pair.

[00106] In another further embodiment, considering the scenario in which the relay UE 115 is in a CONNECTED state and allocated with a dedicated resource in Mode 1 referring to the network scheduled resource allocation, and opposed to Mode 2 which is based on the UE selected autonomous resource allocation, for sending discovery messages, it is proposed that the relay UE 115 is configured to use the resource allocated by the remote UE 110 to respond to the remote UE 110. It is noted that the CONNECTED state means the relay UE is being or is connected to the network and has active UE contexts and bearer services. Here, one could use RRC_CONNNECTED for a known specified state in LTE, although the exemplary embodiments are applicable to other technologies. The response message then indicates the Mode 1 resource that has been allocated for further transaction transmitted from the relay UE 115. In this regard, the proposed procedure above may be applied for initial relay discovery or as a back-up when a wearable remote UE does not have updated knowledge of particular resources a targeted relay UE 115 may potentially use for discovery announcement or response. Thus, the relay UE 115 may use Model A for discovery announcement by default but also monitor for initial discovery request of wearables using Model B. Note that in Model A, there is an announcement message instead of the solicitation messages 210, and the relay UE 115 is an announcing UE, while the remote UEs 110 are monitoring UEs. See, e.g., "Figure 5.3.7.1-1: Public safety direct discovery with Model A" from 3GPP TS 23.303 VI 4.0.0 (2016-09).

[00107] The following are additional examples. Example 1. A method, comprising:

[00108] sending by first user equipment a discovery request comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by a second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by the second user equipment and a wireless communication network; and monitoring by the first user equipment the first wireless resource to determine whether a discovery response is received from the second user equipment.

[00109] Example 2. The method of example 1, further comprising in response to reception of the discovery response, communicating data via direct communications using an established direct communication connection between the first and second user equipment, wherein the data is to be relayed by the second user equipment toward the wireless communication network.

[00110] Example 3. The method of any one of examples 1 or 2, further comprising the first user equipment selecting the first wireless resource from a resource pool comprising the transmission discovery resource pool. [00111] Example 4. The method of example 3, wherein at least part of the resource pool is pre-configured for the first user equipment prior to sending by the first user equipment the discovery request.

[00112] Example 5. The method of any one of examples 3 or 4, further comprising receiving signaling configuring the first user equipment with at least part of the resource pool.

[00113] Example 6. The method of any of examples 1 to 5, wherein the indication of the first wireless resource to be used by the second user equipment comprises one or more indications comprising at least one of the following: a specific resource index from resources of the transmission discovery resource pool; a sub-pool of the transmission discovery resource pool; a set of resource indices from the transmission discovery resource pool; and a set of resource sub-pools from the transmission discovery resource pool.

[00114] Example 7. The method of example 6, wherein the indication of the first wireless resource is provided in the form of an information element in a message.

[00115] Example 8. The method of any of examples 1 to 7, wherein the discovery request is sent using a second wireless resource from a resource pool and wherein the second wireless resource forms part of resources able to be used by the wireless communication network.

[00116] Example 9. The method of any of examples 1 to 8, wherein: the transmission resource pool is part of a resource pool; and the method further comprises: performing for a first time period the monitoring of the first wireless resource to determine whether the discovery response is received from the second user equipment; and in response to not receiving the discovery response in the first time period, for one or more time periods subsequent to the first time period, monitoring at least one additional wireless resource in the resource pool to determine whether the discovery response is received from the second user equipment.

[00117] Example 10. The method of example 9, wherein the monitoring additional wireless resources in the resource pool further comprises monitoring the first wireless resource for at least one of the one or more time periods subsequent to the first time period.

[00118] Example 11. The method of example 9, wherein the monitoring additional wireless resources in the resource pool further comprises monitoring all of the wireless resources in the resource pool for at least one of the one or more time periods subsequent to the first time period.

[00119] Example 12. The method of example 9, wherein the monitoring additional wireless resources in the resource pool further comprises monitoring a gradually increased sub- set of the resources in the resource pool in time periods subsequent to the first time period so that the first user equipment only monitors the first wireless resource for the first time period and monitors more resources in the subsequent time periods. [00120] Example 13. An apparatus, comprising: means for sending by first user equipment a discovery request comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by a second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by the second user equipment and a wireless communication network; and means for monitoring by the first user equipment the first wireless resource to determine whether a discovery response is received from the second user equipment.

[00121] Example 14. The apparatus of example 13, comprising means for performing any of the methods in one of examples 2 to 12.

[00122] Example 15. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus to perform any of the methods in one of examples 1 to 12.

[00123] Example 16. A method, comprising: receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by the second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by a wireless communication network; and sending on the first wireless resource the discovery response from the second user equipment towards the first user equipment.

[00124] Example 17. The method of claim 16, further comprising: communicating data via direct communications on an established direct communications connection between the first and second user equipment; and relaying the communicated data from the second user equipment toward the wireless communication network.

[00125] Example 18. The method of any one of examples 16 or 18, wherein the indication of the first wireless resource to be used by the second user equipment comprises one or more indications comprising at least one of the following: a specific resource index from resources of the transmission discovery resource pool; a sub-pool of the transmission discovery resource pool; a set of resource indices from the transmission discovery resource pool; and a set of resource sub-pools from the transmission discovery resource pool.

[00126] Example 19. The method of claim 18, wherein the indication of the first wireless resource is provided in the form of an information element in a message.

[00127] Example 20. The method of any one of examples 16 to 19, wherein the discovery request is received using a second wireless resource and wherein the second wireless resource forms part of resources able to be used by the wireless communication network. [00128] Example 21. The method of any of one of examples 16 to 20, wherein: the transmission resource pool is part of a resource pool; the sending on the first wireless resource the discovery response is performed within a first time period; and the method further comprises: in response to not receiving a response to sending on the first wireless resource the discovery response, for one or more time periods subsequent to the first time period, sending the discovery response on at least one additional wireless resource in the resource pool.

[00129] Example 22. The method of claim 21, wherein, in response to not receiving the response to sending on the first wireless resource the discovery response, sending the discovery response on the first wireless resource for at least one of the one or more time periods subsequent to the first time period.

[00130] Example 23. The method of claim 21, wherein, in response to not receiving the response to sending on the first wireless resource the discovery response, sending the discovery response on at least one additional wireless resource in the resource pool further comprises selecting a wireless resource from all of the wireless resources in the resource pool and sending the discovery response on the selected wireless resource for at least one of the one or more time periods subsequent to the first time period.

[00131] Example 24. The method of claim 21, wherein, in response to not receiving the response to sending on the first wireless resource the discovery response, sending the discovery response on at least one additional wireless resource in the resource pool further comprises selecting a wireless resource from a gradually increased sub-set of the resources in the resource pool in time periods subsequent to the first time period and transmitting for the time periods the discovery response using the selected wireless resource for a corresponding one of the time period subsequent to the first time period.

[00132] Example 25. The method of any one of examples 21 to 24, wherein a resource pattern is pre-defined so that the second user equipment derives a resource to use to send the discovery response in the subsequent time periods based on the resource used in the first time period.

[00133] 26. An apparatus, comprising: means for receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and comprising an indication of a first wireless resource of a transmission discovery resource pool to be used by the second user equipment to respond to the discovery request, wherein the first wireless resource forms part of resources able to be used by a wireless communication network; and means for sending on the first wireless resource the discovery response from the second user equipment towards the first user equipment.

[00134] Example 27. The apparatus of claim 26, comprising means for performing any of the methods in one of example 18 to 25. [00135] Example 28. A communication system comprising an apparatus of any one of example 13 or 14 and an apparatus of any one of example 26 or 27.

[00136] Example 29. n apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus to perform any of the methods in one of example 16 to 25.

[00137] Example 30. A method, comprising: sending on a first wireless resource and by a first user equipment a discovery request to a second user equipment, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network, and wherein the second user equipment is to determine the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; monitoring the downlink resource to determine whether a discovery response is received from the second user equipment, and in response to reception of the discovery response, communicating data via direct communications between the first and second user equipment, wherein the data is to be relayed by the second user equipment to a network node of the communication system.

[00138] Example 31. The method of claim 30, wherein the pair is associated with a time offset, the first and second wireless resource are a same resource j, the first user equipment sends the discovery request message on the resource j, and the reception of the discovery response is on the resource j but shifted with the time offset in a time domain.

[00139] Example 32. The method of claim 30, wherein the first and second wireless resources for the pair are different resources in a resource pool.

[00140] Example 33. The method of claim 30, wherein the first wireless resource is a resource from a first resource pool and the second wireless resource is a resource from a second resource pool, and wherein the first and second wireless resources are different resources.

[00141] Example 34. An apparatus, comprising: means for sending on a first wireless resource and by a first user equipment a discovery request to a second user equipment, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network, and wherein the second user equipment is to determine the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; means for monitoring the downlink resource to determine whether a discovery response is received from the second user equipment, and means, in response to reception of the discovery response, for communicating data via direct communications between the first and second user equipment, wherein the data is to be relayed by the second user equipment to a network node of the communication system.

[00142] Example 35. The apparatus of claim 34, comprising means for performing any of the methods in one of examples 31 to 33.

[00143] Example 36. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus to perform any of the methods in one of example 30 to 33.

[00144] Example 37. A method, comprising: receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and received on a first wireless resource, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network; determining by the second user equipment the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; sending on the determined second resource the discovery response from the second user equipment toward the first user equipment; communicating data via direct communications on an established direct

communications connection between the first and second user equipment; and relaying the communicated data from the second user equipment to a network node of the communication system.

[00145] Example 38. The method of claim 37, wherein the pair is associated with a time offset, the first and second wireless resource are a same resource j, the second user equipment receives the discovery request message on the resource j, and the sending of the discovery response is on the resource j but shifted with the time offset in a time domain.

[00146] Example 39. The method of claim 37, wherein the first and second wireless resources for the pair are different resources in a resource pool.

[00147] Example 40. The method of claim 37, wherein the first wireless resource is a resource from a first resource pool and the second wireless resource is a resource from a second resource pool, and wherein the first and second wireless resources are different resources.

[00148] Example 41. An apparatus, comprising:

[00149] means for receiving a discovery request sent by a first user equipment, the discovery request received at a second user equipment and received on a first wireless resource, wherein the first wireless resource is part of a pair of resources including a second wireless resource to be used by the second user equipment to respond to the discovery request, wherein the first and second wireless resources form part of resources able to be used by a wireless communication network; means for determining by the second user equipment the second wireless resource based on the pair and use of the first wireless resource to send the discovery request; means for sending on the determined second resource the discovery response from the second user equipment toward the first user equipment; means for communicating data via direct communications on an established direct communications connection between the first and second user equipment; and means for relaying the communicated data from the second user equipment to a network node of the communication system.

[00150] Example 42. The apparatus of claim 41, comprising means for performing any of the methods in one of example 38 to 40.

[00151] Example 43. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus to perform any of the methods in one of example 37 to 40.

[00152] Example 44. A communication system comprising an apparatus of any one of example 34 or 35 and an apparatus of any one of example 41 or 42.

[00153] Example 45. A computer program, comprising code for performing any one of the methods of example 1 to 12, 16 to 25, 30 to 33, or 37 to 40, when the computer program is run on a processor.

[00154] Example 46. The computer program according to claim 45, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

[00155] Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more of the example embodiments disclosed herein is to allow a remote UE to monitor a smaller resource pool than if the exemplary embodiments were not used. Another technical effect of one or more of the example embodiments disclosed herein is reduced power consumption among other benefits, because of the remote UE having to monitor a smaller resource pool than if the exemplary embodiments were not used.

[00156] Embodiments herein may be implemented in software (executed by one or more processors), hardware (e.g., an application specific integrated circuit), or a combination of software and hardware. In an example embodiment, the software (e.g., application logic, an instruction set) is maintained on any one of various conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer, with one example of a computer described and depicted, e.g., in FIG. 1. A computer-readable medium may comprise a computer- readable storage medium (e.g., memories 125, 155, 171 or other device) that may be any media or means that can contain, store, and/or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. A computer-readable storage medium does not comprise propagating signals.

[00157] If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above - described functions may be optional or may be combined.

[00158] Although various aspects are set out above, other aspects comprise other combinations of features from the described embodiments, and not solely the combinations described above.

[00159] It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention.

[00160] The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

3GPP third generation partnership project

5G fifth generation

AP access point

AS access stratum

D2D device to device

DC direct communication

DL downlink (e.g., from eNB to UE)

eNB (or eNodeB) evolved Node B , a base station

ID identification

IE information element

I/F interface

IoT Internet of things

LTE long term evolution

MAC medium access control

MTC machine-type communications

MME mobility management entity

NCE network control element

NA or NW network

ms milliseconds

PLMN public land mobile network

QoS quality of service Rel release

RRH remote radio head

Rx receiver or receiving

SGW serving gateway

SIB system information block

SIM subscriber identity module

TS technical standard

Tx transmitter or transmitting

UE user equipment (e.g., a wireless, typically mobile device)

UL uplink (e.g., from UE to eNB)