WO2013091229A1

WO2013091229A1 - Transparent d2d communications

Info

Publication number: WO2013091229A1
Application number: PCT/CN2011/084510
Authority: WO
Inventors: Wei Bai; Haiming Wang; Chunyan Gao
Original assignee: Renesas Mobile Corporation
Priority date: 2011-12-23
Filing date: 2011-12-23
Publication date: 2013-06-27

Abstract

There is communicated between a first user device and a network access node that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications. A secondary component carrier is then configured for direct communications between the first device and a second device. In various examples: the secondary component carrier is configured as a special SCell in which radio bearers are not used and which lacks a physical broadcast channel and on which synchronization signals are not transmitted; and the network access node signals the first user device to operate on the secondary component carrier as the virtual access node using a C-RNTI assigned to the second user device for addressing data to the second user device.

Description

TRANSPARENT D2D COMMUNICATIONS

TECHNICAL FIELD:

[0001 ] The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs, and more specifically relate to device to device D2D communications directly between user equipments UEs such as one which is D2D-capable and one which is only cellular-capable (sometimes termed transparent D2D). BACKGROUND:

[0002] Acronyms and abbreviations used in this document are expanded below at the end of the section entitled Detailed Description.

[0003] With continuing pressure on wireless network operators to support greater data volumes and numbers of users there is much research recently into D2D communications as a means for improving how efficiently radio resources are utilized. D2D operations may also reduce power consumption at both the network access node and the directly communicating UEs and offer another avenue for networks to offload some of their cellular traffic as well as the possibility of enabling new services in the future. It is anticipated that a new study item for D2D proposed by Qualcomm, Inc. will be soon agreed by the 3GPP members (see document Tdoc-RP- 1 10706 entitled ON THE NEED FOR A 3GPP STUDY ON LTE DEVICE-TO-DEVICE DISCOVERY AND COMMUNICATION; 3 GPP TSG-RAN #52 (plenary); Bratislava, Slovakia; 3 1 May to 3 June 201 1 ).

[0004] From the network operators' perspective it is advantageous to keep control over some aspects of D2D communication, such as link set up step and at least the total radio resources used, in order to control interference and the content transmitted between D2D devices. There are expected to be many types of D2D arrangements, such as a one to one D2D pair, a one-to-M D2D cluster where M is an integer greater than one (meaning one participating device would be a cluster head), and possibly one D2D device communicating with different D2D pairs/clusters simultaneously. There can also be different peak data rates for these different types of D2D networks. To support such different types of D2D communication the participating devices could have different capabilities, in which case it would be important to negotiate/inform of such capability before setup of the D2D in order to assure compatibility between D2D devices. For example, if a first UE is fully D2D capable a compatibility check might find that a second UE is a legacy cellular device without an innate D2D capability (that is, it only supports the cellular mode) and so it is not possible for them to engage in D2D communications, at least not according to many prior art conceptions of how D2D should be implemented. For convenience refer to the above first and second UEs as a D2D UE and a non-D2D legacy UE, respectively.

[0005] In the above example of a D2D UE and a non-D2D legacy UE, if the volume of data between them is large this means that the absence of a D2D option will impose a significant load burden on the cellular radio resource because all data will have to be sent UL to the cellular network by the originating UE only to be re-sent DL from the cellular network to the destination UE. Further, if these two devices are proximal but both of them are at the cell edge there will be an even greater waste of spectrum by using the cellular mode rather than the D2D mode. [0006] If D2D communications are not possible in the above scenario then the benefits of D2D cannot be realized to more than a minimal extent until there is a large population of actual D2D devices. Enabling D2D communications between a D2D UE and a non-D2D legacy UE is sometimes referred to as transparent D2D communications, since it is transparent to the non-D2D legacy UE that the data it exchanges is with another UE (D2D) rather than with a network access node (cellular). In this concept essentially the D2D UE is seen from the perspective of the non-D2D legacy UE as a network access node, but only to the extent of the D2D communications. For example, the non-D2D legacy device would transmit its D2D data on conventional cellular UL logical channels which the D2D device receives, and the D2D device would transmit its D2D data on conventional cellular DL logical channels which the non-D2D legacy device receives. In transparent D2D the true network access node would not be acting to relay the D2D data and so the radio spectrum is not wasted.

[0007] Consider a more specific example of this transparent D2D operation for the LTE system. The D2D UE would have to be capable of sending PDSCHs to the non-D2D legacy UE; generating PHICH for DL feedback; receiving and decoding PUSCHs from the non-D2D legacy UE; decoding PUCCHs from the non-D2D legacy UE (for the case the ACK/NACK is not piggybacked on the PDSCH); generating the related MAC control elements (such as the TA command the eNB traditionally generates); and reading the related MAC control elements from the non-D2D legacy UE (such as buffer status and power headroom reports).

[0008] This is a bit more challenging than it first appears. While the D2D device might send data in a PDSCH format, it will be difficult for the non-D2D legacy device to decode it because the reference signal will be received from the (true) eNB. The D2D UE might be able to generate PHICH information but how can it interleave that with the PDCCH which is sent by the eNB. Additionally, the above concept of transparent D2D does not address how to send the scheduling grant for resources that the D2D communications are to use; whether sent by the D2D UE or by the eNB how does the network maintain control over the scheduling decisions without adding quite a bit of cellular control signaling?

[0009] Some teachings related to D2D operation in the LTE system may be seen at US Patent Publication No. 201 1/0151887 which details specifically D2D operation in a carrier aggregation system. Interference and other considerations determine whether to conduct D2D communications on a secondary component carrier SCell. But this document assumes both participating devices are D2D UEs. Figure 1 illustrates a carrier aggregation arrangement in which the whole system bandwidth is parsed into several component carriers, and each UE in a cell is assigned a primary component carrier PCell and possibly one or more SCells.

SUMMARY: [0010] The foregoing and other problems are overcome, and other advantages are realized, by the use of the exemplary embodiments of this invention.

[001 1 ] In a first exemplary embodiment of the invention there is an apparatus comprising at least one processor and at least one memory storing a computer program. In this embodiment the at least one memory with the computer program is configured with the at least one processor to cause the apparatus to at least: communicate between a first user device and a network access node that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications; and configure a secondary component carrier for direct communications between the first device operating as the virtual network access node and a second device.

[0012] In a second exemplary embodiment of the invention there is a method comprising: communicating between a first user device and a network access node that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications; and configuring a secondary component carrier for direct communications between the first device operating as the virtual network access node and a second device.

[001 3] In a third exemplary embodiment of the invention there is a computer readable memory tangibly storing a computer program executable by at least one processor, the computer program comprising: code for communicating between a first user device and a network access node that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications; and code for configuring a secondary component carrier for direct communications between the first device operating as the virtual network access node and a second device.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0014] Figure 1 is a prior art schematic diagram illustrating component carriers in a wireless radio access technology which utilizes carrier aggregation. [001 5] Figure 2 is a signaling diagram among an eNB and two user devices for setting up and conducting transparent D2D communications according to an exemplary embodiment of these teachings.

[001 6] Figure 3 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with an exemplary embodiment of these teachings. [001 7] Figure 4 is a simplified block diagram of a cellular wireless network access node, and two communicating devices/user equipments communicating using transparent D2D communications, , which are exemplary electronic devices suitable for use in practicing the exemplary embodiments of this invention.

DETAILED DESCRIPTION :

[001 8] The LTE system deploys its total bandwidth as multiple component carriers, of which Figure 1 is an example. Each user in the licensed band is assigned a primary component carrier (PCell) and may be assigned also one or more secondary component carriers (SCell). There are various ways to deploy these component carriers: one or more may be backwards compatible with LTE Release 8 while others may not be due to a lack of some or all control channels or a bandwidth not fitted to the 20 MHz structure of 3GPP Release 8; different component carriers may have different bandwidths; some or all may not be frequency-adjacent to the others; some may have less than a full set of control channels (full set meaning compatible with 3GPP Release 8) or no control channel region at all; and one or more may lie in license-exempt bands. SCell#3 illustrates such a license-exempt component carrier. Carrier aggregation is not limited only to the LTE radio access technology but for more particular detail of these teachings LTE is used in the examples below as a non-limiting environment which can exploit these teachings to advantage.

[001 9] Further to the review of transparent D2D communications above the inventor has determined that much of the difficulties involved arise from the fact that the transparent D2D communication is happening on the same component carrier as the cellular communications. To mitigate those issues, according to these teachings when transparent D2D communications are put into effect they are initialized on a new component carrier on which cellular communications are not ongoing, at least when a D2D device and a non-D2D legacy device are intending to setup a direct link among themselves. That it is transparent D2D communications means that the fact the link is D2D is transparent to the non-D2D legacy device which communicates with the D2D device as if it were a network access node. The D2D device itself is fully capable of (non-transparent) D2D communications directly with a peer terminal, such as for example it is capable of sending and receiving D2D discovery signals. The description below assumes there is one D2D device and one non-D2D legacy device, but of course these teachings can be used to setup a transparent D2D link between two D2D devices if for some reason a conventional D2D network between them is not the most suitable option. Note that this transparent D2D link may be seen from the perspective of the non-D2D legacy device only as a direct link; it may not appreciate that it is in fact a D2D link and thus it is 'transparent' .

[0020] For a practical implementation it is useful that the cellular network which controls the radio resources be able to distinguish whether the D2D network being setup is for transparent D2D or for conventional (non-transparent) D2D. To this end there is defined a new capability for the D2D device that it is capable of transparent D2D, generally sending messages on some DL physical channels and receiving/decoding messages on some physical UL channels. For specific implementation in the LTE system using carrier aggregation, this means the D2D device is capable of sending PDSCHs, PDCCHs, PHICHs, PCFICHs and reference signals and is capable of generating a timing advance command. As to UL, signaling the network that the D2D device has this transparent D2D capability means it is able to receive and decode PUSCHs, PUCCHs, and PRACHs, as well as decode the related MAC control elements such as the buffer status reports and power headroom reports. In one particular embodiment this D2D device need not support a scheduling function itself. The eNB in this embodiment will still schedule the time and frequency radio resources for the D2D data exchange, and the D2D device may only decide which modulation and coding scheme to use for the D2D resources scheduled by the eNB. [0021 ] Once the eNB determines that to enable a transparent D2D communication between a D2D UE and a non-D2D legacy UE is beneficial (for example, if the volume of D2D data justifies the control overhead of setting up the D2D network meaning it is spectrally more efficient), and it determines that the D2D UE has the requisite transparent D2D capability, the eNB can initialize a "transparent D2D communication" on a new component carrier. By example, this new carrier may be a guard band, or it may be some frequency band that is reserved beforehand in case there is a need for transparent D2D.

[0022] The eNB will then configure the two (or more) participating UEs for the new carrier; this will be a new SCell from the perspective of the non-D2D legacy UE and simply an allocated D2D resource from the perspective of the D2D UE which to them will be a SCell. In one embodiment it will be a new carrier type since it will lack the primary broadcast channel PBCH, primary synchronization signal PSS and secondary synchronization signal SSS. The D2D device could then transmit the signaling at the DL reception timing from the cellular network, to ensure the timing difference between PCell and this newly configured SCell is smaller than 31.3μ8 (a requirement under 3GPP Release 10). The eNB then configures the corresponding D2D device to operate on the new carrier as a virtual eNB. The eNB additionally indicates to the non-D2D legacy UE its assigned C-RNT1.

[0023] Preferably the (true) eNB will send all the necessary DL setup signaling to at least the non-D2D UE prior to the time when the non-D2D legacy UE accesses this newly configured SCell. Specifically, all this DL setup signaling such as the activate (and deactivate) commands to turn on (and off) the SCell will be sent by the eNB to the non-D2D legacy UE on the PCell.

[0024] Now the new radio resource is setup for both devices, which as noted above the non-D2D legacy device sees as a newly configured SCell and the D2D device sees as an allocation of dedicated D2D resources. The D2D device will send its D2D data to the non-D2D legacy UE as if the D2D UE were a conventional eNB. The D2D UE will send the common reference signal CRS on this newly configured SCell and will generate a PDCCH addressed to the non-D2D legacy UE's C-RNTI, For the case in which the PDCCH schedules a DL resource on the SCell for the non-D2D legacy UE, the D2D UE will then also send a PDSCH to the non-D2D legacy UE on that scheduled resource. [0025] On the UL portions of the transparent D2D the D2D device will receive data from the non-D2D legacy UE as if the D2D device were an eNB. The D2D device will decode the PUSCH sent by the non-D2D legacy UE which carries its D2D data. Once the D2D UE is configured, it should whenever possible always give the UL grant to the non-D2D legacy UE on the subframe where there could be an ACK/NACK transmission. This will allow the PUSCH to piggyback the ACK/NACK information because there will be no PUCCH on the SCell, only the PCell. With that in mind the eNB should not configure simultaneous PUSCH and PUCCH for the D2D UE. [0026] Since the D2D device will always give the UL grant to the corresponding non-D2D legacy UE, in an exemplary embodiment the BSR will always have already been reported so there is no issue with the scheduling request even though it is only on the PCell and not on the SCell. [0027] Once the D2D session is finished, the D2D device can then indicate that fact to the eNB which allows the eNB to release the corresponding SCell configuration. The non-D2D legacy UE can also report the completion of the D2D session (e.g., that the SCell is no longer needed since the D2D nature of the exchange is transparent to the non-D2D legacy UE), and in this case the non-D2D legacy UE can report this on the PCell to be received by the eNB and/or on the SCell to be received by the D2D UE. [0028] In this manner D2D communication between a D2D device and a non-D2D legacy device are enabled. If in addition there is a need for the non-D2D legacy UE to communicate with the eNB while the D2D link is setup, there are a few other issues to solve. The DL transmissions to the non-D2D legacy UE are simple because in this scenario the DL transmissions will be coming from two different transmitters, the D2D device and the eNB. The UL transmissions are a bit more challenging because in the current LTE mechanism the decision how to fill the UL grant with UL data depends on the particular UE's implementation and on some general rules such as Logic Channel Prioritization (LCP). To avoid the non-D2D legacy UE sending to the eNB the UL data which is intended for the D2D device (or vice versa), the logic channel prioritization can always be set so that channels to the eNB always have a higher priority than channels to the D2D UE whenever both transparent D2D and cellular links are active at once. For UL feedback, if the UL data carries ACK/NACK feedback information for DL transmissions from both the eNB and the D2D device, it is preferable to send the ACK/NACK feedback that corresponds to a particular DL transmission to the corresponding transmitter (eNB or D2D UE) rather than aggregate both feedbacks in a single message.

[0029] For signaling the SCell configuration for the non-D2D legacy UE, the eNB should also configure whether the current SCell is a "special SCell" and indicate which services are allowed and which are prohibited in that SCell. In this manner the non-D2D legacy UE can distinguish between the two types of services: (radio bearers) on a conventional component carrier (whether PCell or another SCell) and D2D communications on the "special SCell".

[0030] When reporting its BSR on a normal (not special) cell, the non-D2D legacy UE should only calculate and report the buffer status of the service which is supposed to be transmitted on that normal cell, and it should also only calculate and report the buffer status of the service which is supposed to be transmitted on the D2D "special SCell" when reporting its BSR on that special SCell.

[0031 ] When report ACK/NACK information for a DL transmission, the non-D2D legacy UE should report its ACK NACK for any DL transmission received on a normal/non-special cell on the PCell, and should report its ACK/NACK for any DL transmission received on the special SCell on that same SCell. And also the eNB should configure simultaneous PUSCH and PUCCH for the non-D2D legacy UE, or always schedule UL transmission on the PCell as well to enable ACK NACK transmission from the non-D2D legacy UE for its normal cellular/non D2D transmissions. These special SCell procedures might require some minor modifications to the non-D2D legacy UE but these are quite minor and can be easily done via a wireless software update in order to implement these particular teachings for legacy devices.

[0032] There is a minor consideration as to propagation delay. The non-D2D legacy UE may see a different propagation delay to the eNB and to the D2D UE, in which case the non-D2D legacy UE would need to support multiple timing advances. Most do but not all, and it is expected to be a requirement for 3GPP Release 1 1 so over time this requirement will continue to decline in importance. Also, to have a transparent D2D communication for the non-D2D legacy UE the eNB will need to configure two carriers if that UE is operating under the TDD mode (an UL and a DL component carrier respectively), but only one component carrier for if it is operating in the TDD mode. These are in addition to the PCell.

[0033] The above examples for implementing transparent D2D communication in the LTE system are shown in the signaling diagram of Figure 2. The various nodes eNB 24, D2D device 20 and non-D2D legacy device 22 (labeled normal device in Figure 2) are detailed schematically at Figure 3. At message 202 of Figure 2 the D2D device 20 reports its D2D capability to the eNB 24. From this the eNB knows that the D2D device can operate as a virtual network access node for transparent D2D communications. Once there is some requirement or need for communication between the D2D device 20 and another normal UE 22, they each report their respective buffer status to the eNB at messages 204 and 206, which may in an embodiment also carry channel quality information CQI. After the eNB 24 receives the BSR from both the D2D device 20 and the normal UE 22, the eNB 24 then determines whether or not to utilize the transparent D2D communication at block 208. This decision depends on the relative spectrum efficiency which could be achieved by direct D2D between the devices 20, 22 or by cellular links with the eNB 24 acting essentially as a data relay between the proximal devices 20, 22.

[0034] Once the eNB 24 decides at block 208 to use the transparent D2D communication, it first configures the D2D device 20 to act (with respect to the normal device 22) like a virtual eNB on the configured carrier/SCell at message 210. From this message the D2D device 20 knows to continuously send CRSs on the newly configured SCell. The eNB also configures the normal UE 22 for this new SCell, which does not have a PBCH or any PSS/SSS. In order to best conserve spectrum the bandwidth of this newly configured SCell depends on the buffer status which were reported earlier at messages 204 and 206. To ensure compatibility with the UEs 20, 22, the eNB 24 should set the bandwidth of this new SCell within the current allowed bandwidths (e.g., not in the license exempt spectrum in case the normal UE 22 is not capable of operating there using LTE signaling protocols). As noted above it is possible to use the guard band for this transparent D2D SCell because the transmit power for D2D communications is not expected to be high and will therefore cause less interference to the regular cellular system channels.

[0035] The eNB 24 then activates the SCell with an activation command at message 21 6. In an alternative embodiment the D2D device 20 can send this command 216 to the normal device 22 (and also to the eNB 24 by way of keeping it informed). [0036] In some embodiments the normal device 22 will send to the D2D device 20 (and/or vice versa) on the configured and activated SCell at message 218 some MAC control elements such as the timing advance command and/or the power headroom report as noted above. Finally at message 220 the D2D device 20 sends its D2D data to the normal UE 22 with a DL format, and schedules on the total bandwidth an UL transmission from the normal UE 22.

[0037] Once the D2D service is completed at 222, the D2D device 20 then reports that information to the eNB 24 at message 224. The normal UE 22 might also report termination of the D2D service and in this case the reporting may be on either the PCell or the SCell but if the SCell there is a chance the eNB 24 might not receive it due to the hidden node problem (that is, due to relative positions the normal device 22 might be visible to the D2D device 20 but not to the eNB 24). Finally the eNB 24 releases the SCell configuration for the D2D UE at message 226 and also releases the corresponding configuration of the normal device 22 at message 228.

[0038] One technical effect of certain embodiments of these teachings is that they enable D2D communications even if one of the devices 22 doesn't support such a function. The transparent D2D communications detailed by example herein may be used to significantly improve the communication efficiency particularly when the D2D device 20 and the normal UE 22 are both at the cell edge. One significant technical effect is that there is little added complexity over current LTE signaling regimens and so these teachings may be implemented in practical systems with little change to currently adopted procedures.

[0039] Now are detailed with reference to Figure 3 further particular exemplary embodiments from the perspective of the eNB and from the D2D device. Without loss of generality Figure 3 refers to the eNB as a network access node, to the D2D UE as a first user device, and to the UE in the position of the non-D2D UE as the second user device. Figure 3 may be performed by the whole eNB 24 or the whole first user device 20 shown at Figure 4, or by one or several components thereof such as a modem. At block 302 there is some communication between a first user device and a network access node which establishes that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications. From the perspective of the eNB it receives this communication and from the perspective of the first user device it sends it, shown by example at Figure 2 as message 202. And at block 304 a secondary component carrier is configured for direct communications between the first device operating as the virtual network access node and a second device. While the eNB does this in message 210 carrier upon receiving that message 210.

[0040] Further portions of Figure 3 represent various of the specific but non-limiting embodiments detailed above. Block 306 summarizes the exemplary embodiment in which the secondary component carrier is configured as a special cell SCell in which radio bearers are not used, and which lacks a physical broadcast channel PBCH and on which synchronization signals PSS/SSS are not transmitted.

[0041 ] Block 308 stipulates that Figure 3 is from the perspective of the network access node/eNB 24, and adds the further step of the eNB signaling the first user device to operate on the secondary component carrier as the virtual access node and address data to the second user device using a cell radio network temporary identifier C-RNTI assigned to the second user device. [0042] Block 310 stipulates that Figure 3 is from the perspective of the first user device/D2D device 20, and adds the further step of the first user device operating on the secondary component carrier as the virtual access node by transmitting on the secondary component carrier at least one of common reference signals CRSs; resource allocations (PDCCHs) addressed to a C-RNTI assigned to the second user device; and data on a physical downlink shared channel PDSCH that is directed to the second user device. Other indications that the first/D2D device is operating as a virtual eNB is that it sends to the C-RNTI of the second/non-D2D device either or both of: hybrid automatic repeat request indictors (on the PHICH); and an indication of how long is a physical downlink control channel (PDCCH length sent on the PCFICH). Additionally the first user device may operate as the virtual eNB on the secondary component carrier by decoding a physical uplink shared channel PUSCH received from the second user device.

[0043] Block 312 further has the first user device signaling to the network access node that the direct (transparent D2D) communications are complete and in reply receiving from the network access node a message releasing the secondary component carrier. [0044] Figure 3 is a logic flow diagram which may be considered to illustrate the operation of a method, and a result of execution of a computer program stored in a computer readable memory, and a specific manner in which components of an electronic device are configured to cause that electronic device to operate. The various blocks shown in Figure 4 may also be considered as a plurality of coupled logic circuit elements constructed to carry out the associated function(s), or specific result of strings of computer program code stored in a memory. [0045] Such blocks and the functions they represent are non-limiting examples, and may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

[0046] Reference is now made to Figure 4 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing the exemplary embodiments of this invention. In Figure 4 there is a first (D2D) UE 20 or device operating in the LTE system under an eNB 24 via wireless link 21 , and there is also a second (non D2D legacy) UE 22 or device operating under the eNB 24 via wireless link 23. For completeness there is also shown a higher network node for the LTE system, namely a mobility management entity MME 26 which provide connectivity with further networks such as for example a publicly switched telephone network PSTN and/or a data communications network/Internet via a S I 1 interface to a gateway, and it may also have a S 10 interface to other MMEs. There is also a data and/or control path S I coupling the eNB 24 with the MME 26.

[0047] The first device 20 includes processing means such as at least one data processor (DP) 20A, storing means such as at least one computer-readable memory (MEM) 20B storing at least one computer program (PROG) 20C, communicating means such as a transmitter TX 20D and a receiver RX 20E for bidirectional wireless communications with the eNB 24 and with the second device 22 via one or more antennas 20F. While only one transmitter and receiver are shown it is understood there may be more than one. Inherent in the first device is also a clock from which various software-defined timers are run. Also stored in the MEM 20B at reference number 20G is the rules and signaling protocol shown at Figure 2 for transparent D2D communications and for operating as a virtual eNB. The second device 22 is functionally similar with blocks 22A, 22B, 22C, 22D, 242 and 22F. The first and second devices 20, 22 communicate with one another directly according to the various described embodiments using the direct wireless link 25.

[0048] The eNB 24, or more generally the network access node/serving cell, also includes processing means such as at least one data processor (DP) 24A, storing means such as at least one computer-readable memory (MEM) 24B storing at least one computer program (PROG) 24C, and communicating means such as a transmitter TX 24D and a receiver RX 24E for bidirectional wireless communications with the UEs 20, 22 via one or more antennas 24F. The eNB 22 also stores in its memory at 22G the rules and signaling protocol shown at Figure 2 for transparent D2D communications from its perspective. The MME 26 also has its own MEM 26B storing a PROG 26C executable by a DP 26A.

[0049] While not particularly illustrated for the user devices 20, 22 or the network access node 24, those apparatus are also assumed to include as part of their wireless communicating means a modem which may be inbuilt on an RF front end chip within those devices 20, 22, 24 and which also carries the TX 20D/22D/24D and the RX 20E/22E/24E. Such a modem 26D/E is shown for the MME 26.

[0050] At least one of the PROGs 20C/24C in the first device and the eNB 24 is assumed to include program instructions that, when executed by the associated DP 20A/24A, enable the device/eNB to operate in accordance with the exemplary embodiments of this invention, as was discussed above in detail. In these regards the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 20B/24B which is executable by the DP 20A of the device 20 and/or by the DP 24A of the network access nodes 24; or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Electronic devices implementing these aspects of the invention need not be the entire apparatus 20, 24 as shown, but exemplary embodiments may be implemented by one or more components of same such as the above described tangibly stored software, hardware, firmware and DP, or a system on a chip SOC or an application specific integrated circuit ASIC or a digital signal processor DSP.

[0051 ] In general, the various embodiments of the first device 20 can include, but are not limited to: data cards, USB dongles, user equipments, cellular telephones; personal portable digital devices having wireless communication capabilities including but not limited to laptop/palmtop/tablet computers, digital cameras and music devices, Internet appliances, remotely operated robotic devices or machine-to-machine communication devices.

[0052] Various embodiments of the computer readable MEMs 20B/22B/24B/26B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 20A/22A/24A/26A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.

[0053] Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. While the exemplary embodiments have been described above in the context of the E-UTRAN (LTE/LTE-A) system, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system, and that they may be used to advantage in other wireless communication systems such as for example WCDMA, UTRAN and others which operate or are adapted in the future to operate using multiple component carriers.

[0054] Some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

[0055] The following acronyms and abbreviations found in the specification and/or the drawing figures are defined as follows:

BSR buffer status report

CE control element

CRS common reference signal

D2D device to device

DL downlink

E-UTRA Evolved Universal Terrestrial Radio Access

eNB evolved NodeB (base station of an E-UTRA network)

GPS global positioning system

HARQ hybrid automatic repeat request

LTE long term evolution

LTE-A long term evolution advanced

MAC medium access control

PBCH physical broadcast channel

PCF1CH physical control format indicator channel

PDCCH physical downlink control channel

PDSCH physical downlink shared channel

PHICH physical HARQ indicator channel

PHR power headroom report

PSS primary synchronization signal PUCCH physical uplink control channel

PUSCH physical uplink shared channel

Rx reception/receiver

SSS secondary synchronization signal TA timing advance

Tx transmission/transmitter

UE user equipment

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising:

at least one processor and at least one memory storing a computer program; in which the at least one memory with the computer program is configured with the at least one processor to cause the apparatus to at least:

communicate between a first user device and a network access node that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications; and

configure a secondary component carrier for direct communications between the first device operating as the virtual network access node and a second device.

2. The apparatus according to claim 1 , in which the secondary component carrier is configured as a special SCell in which radio bearers are not used and which lacks a physical broadcast channel and on which synchronization signals are not transmitted.

3. The apparatus according to claim 1 , in which the apparatus comprises the network access node and the at least one memory with the computer program is configured with the at least one processor to cause the network access node further to signal the first user device to operate on the secondary component carrier as the virtual access node using a cell radio network temporary identifier assigned to the second user device for addressing data to the second user device.

4. The apparatus according to claim 1 , in which the apparatus comprises the first user device and the at least one memory with the computer program is configured with the at least one processor to cause the first user device further to operate on the secondary component carrier as the virtual access node by transmitting on the secondary component carrier at least one of:

common reference signals;

resource allocations addressed to a cell radio network temporary identifier assigned to the second user device;

hybrid automatic repeat request indictors; an indication of how long is a physical downlink control channel; and data on a physical downlink shared channel directed to the second user device.

5. The apparatus according to claim 4, in which the at least one memory with the computer program is configured with the at least one processor to cause the first user device further to operate on the secondary component carrier as the virtual access node by decoding a physical uplink shared channel received from the second user device.

6. The apparatus according to claim 4, in which the at least one memory with the computer program is configured with the at least one processor to cause the first user device further to signal to the network access node that the direct communications are complete and in reply receive from the network access node a message releasing the secondary component carrier.

7. A method comprising:

communicating between a first user device and a network access node that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications; and

configuring a secondary component carrier for direct communications between the first device operating as the virtual network access node and a second device.

8. The method according to claim 7, in which the secondary component carrier is configured as a special SCell in which radio bearers are not used and which lacks a physical broadcast channel and on which synchronization signals are not transmitted.

9. The method according to claim 7, in which the method is executed by the network access node and the method further comprises the network access node signaling the first user device to operate on the secondary component carrier as the virtual access node using a cell radio network temporary identifier assigned to the second user device for addressing data to the second user device.

10. The method according to claim 7, in which the method is executed by the first user device and the method further comprises the first user device operating on the secondary component carrier as the virtual access node by transmitting on the secondary component carrier at least one of:

common reference signals;

hybrid automatic repeat request indictors;

an indication of how long is a physical downlink control channel; and data on a physical downlink shared channel directed to the second user device.

1 1. The method according to claim 10, in which the method further comprises the first user device operating on the secondary component carrier as the virtual access node by decoding a physical uplink shared channel received from the second user device.

12. The method according to claim 10, in which the method further comprises the first user device signaling to the network access node that the direct communications are complete and in reply receiving from the network access node a message releasing the secondary component carrier.

13. A computer readable memory tangibly storing a computer program executable by at least one processor, the computer program comprising:

code for communicating between a first user device and a network access node that the first user device is capable of operating as a virtual network access node for transparent device-to-device D2D communications; and

code for configuring a secondary component carrier for direct communications between the first device operating as the virtual network access node and a second device.

14. The computer readable memory according to claim 13, in which the secondary component carrier is configured as a special SCell in which radio bearers are not used and which lacks a physical broadcast channel and on which synchronization signals are not transmitted.

15. The computer readable memory according to claim 13, in which the computer readable memory and the at least one processor are disposed in the network access node, and the computer program further comprises code for signaling the first user device to operate on the secondary component carrier as the virtual access node using a cell radio network temporary identifier assigned to the second user device for addressing data to the second user device.

16. The computer readable memory according to claim 13, in which the computer readable memory and the at least one processor are disposed in the first user device and the computer program further comprises code for operating on the secondary component carrier as the virtual access node by transmitting on the secondary component carrier at least one of:

common reference signals;

hybrid automatic repeat request indictors;

17. The computer readable memory according to claim 16, in which the code for operating on the secondary component carrier as the virtual access node further comprises code for decoding a physical uplink shared channel received from the second user device.

18. The computer readable memory according to claim 16, in which the computer program further comprises code for signaling to the network access node that the direct communications are complete and in reply receiving from the network access node a message releasing the secondary component carrier.