Transmit power adjustment for inter-device communication in wireless communication systems

The present disclosure generally relates to communications in wireless communication systems, and more particularly, to transmit power adjustment for inter-device communications in wireless communication systems.

In wireless networks such as Long Term Evolution (LTE) and LTE-Advanced communication networks, a user equipment (UE) may communicate with other UEs via a base station and an evolved packet core (EPC) network. For example, a UE may send data packets to its serving base station on an uplink. The serving base station may forward the data packets to the EPC network and the EPC network may forward the data packet to another base station or to the same base station that is serving another UE. Data transfer between the UEs is routed through the base station and the EPC. The communication between the UEs is controlled by the policies set by the operator administering the network.

The UEs may communicate directly with each other using other radio access technology (RAT), such as, wireless local area network (WLAN) or Bluetooth when the UEs are located in close proximity and have access to the other RAT. However, this multi-RAT communication requires the availability of the other RAT and the capability of the UEs to operate in the other RAT. Moreover, handover from cellular technology to other RATs may result in service interruption and dropped calls.

The accompanying drawings, which are incorporated in and constitute part of this specification, and together with the description, illustrate and serve to explain various examples.

FIG. 1 illustrates an example cellular wireless communication system in which methods and systems consistent with the present disclosure may be implemented.

FIG. 2 illustrates an example access node device, in accordance with an example of the present disclosure.

FIG. 3 illustrates an example user equipment device, in accordance with an example of the present disclosure.

FIG. 4 illustrates a flow diagram of an example method for adjusting a device transmit power for inter-device communication, in accordance with an example of the present disclosure.

FIG. 5 illustrates a flow chart of an example method for adjusting a device transmit power level for inter-device communication, in accordance with an example of the present disclosure.

FIG. 6 illustrates a flow diagram of another example method for adjusting a device transmit power for inter-device communication, in accordance with an example of the present disclosure.

The present disclosure is directed to systems, methods, and apparatuses for inter-device communication in cellular wireless communication systems. In the current cellular communication system, data transfer between UEs has to be routed through a base station and a core network. When UEs located in close proximity communicate with each other, it would be advantageous for the UEs to communicate via a direct inter-device communication link between them, instead of transferring the data via a network. By providing a direct inter-device communication link between the UEs, improved overall spectral efficiency may be achieved. Moreover, the direct link between the UEs requires lower transmit power at the UE compared to transmitting to the base station, thereby resulting in battery savings at the UEs. Additionally, communicating over the direct link between the UEs may improve quality of service (QoS).

Although the UE may be able to communicate over a direct communication link using another RAT, such as, WLAN, Bluetooth, etc., it requires availability of the services of the other RAT and also requires implementation of the other RAT at the UE. Furthermore, service interruptions and dropped calls may result from switching or handover between different RATs. Therefore, it may be advantageous to enable communications over the inter-device communication link using the same cellular radio access technology and operating in the same radio band.

Reference will now be made in detail to example approaches implemented according to the disclosure; the examples are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 1 illustrates an example cellular wireless communication system 100 in which systems and methods consistent with this disclosure may be implemented. The cellular network system 100 shown in FIG. 1 includes one or more base stations (i.e., 112 a and 112 b ). In the LTE example of FIG. 1 , the base stations are shown as evolved Node Bs (eNBs) 112 a and 112 b , although base stations operate in any wireless communications system, including for example, macro cell, femto cell, relay cell, and pico cell. Base stations are nodes that can relay signals for mobile devices, also referred to herein as user equipment, or for other base stations. The base stations are also referred to as access node devices. The example LTE telecommunications environment 100 of FIG. 1 includes one or more radio access networks 110 , core networks (CNs) 120 , and external networks 130 . In certain implementations, the radio access networks may be Evolved Universal Terrestrial Radio Access Networks (EUTRANs). In addition, core networks 120 may be evolved packet cores (EPCs). Further, as shown, one or more mobile electronic devices 102 a , 102 b operate within the LTE system 100 . In some implementations, 2G/3G systems 140 , e.g., Global System for Mobile communication (GSM), Interim Standard 95 (IS-95), Universal Mobile Telecommunications System (UMTS) and Code Division Multiple Access (CDMA2000) may also be integrated into the LTE telecommunication system 100 .

In the example LTE system shown in FIG. 1 , the EUTRAN 110 includes eNB 112 a and eNB 112 b . Cell 114 a is the service area of eNB 112 a and Cell 114 b is the service area of eNB 112 b . User equipment (UEs) 102 a and 102 b operate in Cell 114 a and are served by eNB 112 a . The EUTRAN 110 can include one or more eNBs (e.g., eNB 112 a and eNB 112 b ) and one or more UEs (e.g., UE 102 a and UE 102 b ) can operate in a cell. The eNBs 112 a and 112 b communicate directly to the UEs 102 a and 102 b . In some implementations, the eNB 112 a or 112 b may be in a one-to-many relationship with the UEs 102 a and 102 b , e.g., eNB 112 a in the example LTE system 100 can serve multiple UEs (i.e., UE 102 a and UE 102 b ) within its coverage area Cell 114 a , but each of UE 102 a and UE 102 b may be connected to one serving eNB 112 a at a time. In some implementations, the eNBs 112 a and 112 b may be in a many-to-many relationship with the UEs, e.g., UE 102 a and UE 102 b can be connected to eNB 112 a and eNB 112 b . The eNB 112 a may be connected to eNB 112 b such that handover may be conducted if one or both of the UEs 102 a and 102 b travels, e.g., from cell 114 a to cell 114 b . The UEs 102 a and 102 b may be any wireless electronic device used by an end-user to communicate, for example, within the LTE system 100 .

The UEs 102 a and 102 b may transmit voice, video, multimedia, text, web content and/or any other user/client-specific content. The transmission of some content, e.g., video and web content, may require high channel throughput to satisfy the end-user demand. In some instances, however, the channel between UEs 102 a , 102 b and eNBs 112 a , 112 b may be contaminated by multipath fading due to the multiple signal paths arising from many reflections in the wireless environment. Accordingly, the UEs' transmission may adapt to the wireless environment. In short, the UEs 102 a and 102 b may generate requests, send responses or otherwise communicate in different means with Evolved Packet Core (EPC) 120 and/or Internet Protocol (IP) networks 130 through one or more eNBs 112 a and 112 b.

In some implementations, the UEs 102 a and 102 b may communicate over an inter-device communication link when they are located in close proximity to one another, without routing the data through the eNB 112 a . The boundary of the distance of the inter-device communication link may be limited by the transmission power of the UEs. In one example, close proximity could be a few meters. In another example, close proximity could be tens of meters. It is also possible that in certain circumstances, the close proximity may mean larger distance such as hundreds of meters. For example, the UEs 102 a and 102 b may communicate directly over the inter-device communication link 104 , instead of communicating with each other through their links with the eNB 112 a , i.e., 106 and 108 respectively. The inter-device communication link may also be referred to as a device-to-device (D2D) communication link. The UEs 102 a and 102 b may simultaneously maintain an active communication link with the eNB 112 a such that the UEs 102 a and 102 b may still receive messages from the eNB or other UEs, when communicating with each other over the direct inter-device link.

Examples of UEs include, but are not limited to, a mobile phone, a smart phone, a telephone, a television, a remote controller, a set-top box, a computer monitor, a computer (including a tablet computer such as a BlackBerry® Playbook tablet, a desktop computer, a handheld or laptop computer, a netbook computer), a personal digital assistant (PDA), a microwave, a refrigerator, a stereo system, a cassette recorder or player, a DVD player or recorder, a CD player or recorder, a VCR, an MP3 player, a radio, a camcorder, a camera, a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wristwatch, a clock, a game device, etc. The UE 102 a or 102 b may include a device and a removable memory module, such as a Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity Module (SIM) application, a Universal Subscriber Identity Module (USIM) application, or a Removable User Identity Module (R-UIM) application. Alternatively, the UE 102 a or 102 b may include the device without such a module. The term “UE” can also refer to any hardware or software component that can terminate a communication session for a user. In addition, the terms “user equipment,” “UE,” “user equipment device,” “user agent,” “UA,” “user device,” and “mobile device” can be used synonymously herein.

A radio access network is part of a mobile telecommunication system which implements a radio access technology, such as Universal Mobile Telecommunications System (UMTS), CDMA2000 and 3rd Generation Partnership Project (3GPP) LTE. In many applications, the Radio Access Network (RAN) included in an LTE telecommunications system 100 is called an EUTRAN 110 . The EUTRAN 110 can be located between the UEs 102 a , 102 b and EPC 120 . The EUTRAN 110 includes at least one eNB 112 a or 112 b . The eNB can be a radio base station that may control all, or at least some, radio related functions in a fixed part of the system. One or more of eNB 112 a or 112 b can provide radio interface within their coverage area or a cell for the UEs 102 a , 102 b to communicate. The eNBs 112 a and 112 b may be distributed throughout the cellular network to provide a wide area of coverage. The eNBs 112 a and 112 b may directly communicate with one or more UEs 102 a , 102 b , other eNBs, and the EPC 120 .

The eNBs 112 a and 112 b may be the end point of the radio protocols towards the UEs 102 a , 102 b and may relay signals between the radio connection and the connectivity towards the EPC 120 . The communication interface between the eNB and the EPC is often referred to as an S 1 interface. In certain implementations, EPC 120 is a central component of a core network (CN). The CN can be a backbone network, which may be a central part of the telecommunications system. The EPC 120 can include a mobility management entity (MME), a serving gateway (S-GW), and a packet data network gateway (PGW). The MME may be the main control element in the EPC 120 responsible for the functionalities comprising the control plane functions related to subscriber and session management. The SGW can serve as a local mobility anchor, such that the packets are routed through this point for intra EUTRAN 110 mobility and mobility with other legacy 2G/3G systems 140 . The S-GW functions may include user plane tunnel management and switching. The PGW may provide connectivity to the services domain comprising external networks 130 , such as the IP networks. The UEs 102 a , 102 b , EUTRAN 110 , and EPC 120 are sometimes referred to as the evolved packet system (EPS). It is to be understood that the architectural evolvement of the LTE system 100 is focused on the EPS. The functional evolution may include both EPS and external networks 130 .

Though described in terms of FIG. 1 , the present disclosure is not limited to such an environment. In general, cellular telecommunication systems may be described as cellular networks made up of a number of radio cells, or cells that are each served by a base station or other fixed transceiver. The cells are used to cover different locations in order to provide radio coverage over an area. Example cellular telecommunication systems include Global System for Mobile Communication (GSM) protocols, Universal Mobile Telecommunications System (UMTS), 3GPP Long Term Evolution (LTE), and others. In addition to cellular telecommunication systems, wireless broadband communication systems may also be suitable for the various implementations described in the present disclosure. Example wireless broadband communication systems include IEEE 802.11 WLAN, IEEE 802.16 WiMAX network, etc.

FIG. 2 illustrates an example access node device 200 consistent with certain aspects of this disclosure. The access node device 200 includes a processing module 202 , a wired communication subsystem 204 , and a wireless communication subsystem 206 . The processing module 202 can include one or more processing components (alternatively referred to as “processors” or “central processing units” (CPUs)) operable to execute instructions associated with managing IDC interference. The processing module 202 can also include other auxiliary components, such as random access memory (RAM), read only memory (ROM), secondary storage (for example, a hard disk drive or flash memory). Additionally, the processing module 202 can execute certain instructions and commands to provide wireless or wired communication, using the wired communication subsystem 204 or a wireless communication subsystem 206 . One skilled in the art will readily appreciate that various other components can also be included in the example access node device 200 without departing from the principles of the present disclosure.

FIG. 3 illustrates an example user equipment device 300 consistent with certain aspects of the present disclosure. The example user equipment device 300 includes a processing unit 302 , a computer readable storage medium 304 (for example, ROM or flash memory), a wireless communication subsystem 306 , a user interface 308 , and an I/O interface 310 .

The processing unit 302 may include components and perform functionality similar to the processing module 202 described with regard to FIG. 2 . The wireless communication subsystem 306 may be configured to provide wireless communications for data information or control information provided by the processing unit 302 . The wireless communication subsystem 306 can include, for example, one or more antennas, a receiver, a transmitter, a local oscillator, a mixer, and a digital signal processing (DSP) unit. In some implementations, the wireless communication subsystem 306 may receive or transmit information over a direct inter-device communication link. In some implementations, the wireless communication subsystem 306 can support MIMO transmissions.

The user interface 308 can include, for example, one or more of a screen or touch screen (for example, a liquid crystal display (LCD), a light emitting display (LED), an organic light emitting display (OLED), a microelectromechanical system (MEMS) display, a keyboard or keypad, a tracking device (e.g., trackball, trackpad), a speaker, and a microphone).

The I/O interface 310 can include, for example, a universal serial bus (USB) interface. One skilled in the art will readily appreciate that various other components can also be included in the example UE device 300 .

For UEs to communicate over a direct inter-device communication link, an inter-device communication link is enabled between the UEs. The direct inter-device communication link allows data exchange between the UEs, without routing through the base station and the core network. Descriptions will now be made about methods for UE transmit power adjustment for the inter-device communication in the cellular wireless communication system, according to certain examples of the present disclosure.

The UE may adjust its transmit power for transmissions over the inter-device communication link during a device handshake/discovery procedure and/or during the data transmission. For example, a UE may determine whether to adjust a transmit power level based on a data exchange between the UE and at least one other UE over an inter-device communication link, and adjust the transmit power level based on the determination. The transmit power can be slowly controlled, e.g., in tens of radio frames or can be fast controlled, e.g., in the subframe level. The power control could be eNB based, UE based or both. In one example, eNB could directly control the transmission power based on the feedback information from the UE. In another example, the UE could directly control the transmission power over the D2D link but in this case, the feedback is needed from another UE. ENB and the UE may also be collaborated for the power control. The power control could be single step or multiple step procedure.

LTE uplink and/or downlink radio resources may be used for the data exchange between the UEs over the inter-device communication link. The UE may start transmitting transmission pattern with a transmit power equal to P mn and increase the transmit power by an increment of Δ TP each time the detection of the predetermined transmission pattern does not meet a required performance target. If the transmit power reaches a maximum transmit power level P mx , or the received signal quality meets the required performance target, the UE may determine not to increase the transmit power.

FIG. 4 illustrates a flow diagram 400 of an example method for adjusting a device transmit power for inter-device communication, in accordance with an example of the present disclosure. As shown in FIG. 4 , the eNB may send respectiveradio resource control (RRC) D2D handshake (HS) Setup messages to UE 0 and UE 1 at 402 and 404 to set up a device handshake procedure. Subsequently, UE 0 and UE 1 may each send a RRC D2D Handshake Setup Response message to the eNB at 406 and 408 , respectively, confirming a reception of the RRC D2D Handshake Setup Message. UE 0 and UE 1 may then start monitoring the messages from the eNB for an initiation of the device handshake procedure. The radio resources for sending these RRC messages may be assigned/granted by the serving eNB via physical downlink shared channel (PDCCH) using the UEs' respective cell radio network temporary identities (C-RNTIs).

Although not shown in FIG. 4 , when the eNB determines that a direct communication link between UE 0 and UE 1 may be enabled, the eNB may send an RRC D2D Connection Setup message to UE 0 and/or UE 1 , prior to the device handshake/discovery procedure. The D2D Connection Setup message may include transmission parameters for the direct communication link, such as a C-RNTI of UE 0 or UE 1 , temporary transmit point identifications for each UE communicating over the inter-device communication link, minimum and/or maximum transmit power levels for transmitting over the inter-device communication link, a device-to-device radio network temporary identity (DD-RNTI) for identifying the direct inter-device link, a transmit power incremental value, Δ TP for the direct inter-device link, a guard time for the direct inter-device link, etc. The D2D Connection Setup message may also include a set of predefined transmission patterns and a target channel quality indicator (CQI). This message may also include an indication of whether the uplink (UL) radio resources or downlink (DL) radio resources are assigned for the inter-device communication. The D2D Connection Setup message may not consist all the above mentioned parameters. Some of these parameter may be sent in the subsequent RRC D2D HS Setup message. Subsequent to receiving the D2D Connection Setup message from the eNB, UE 0 and/or UE 1 may send a D2D Connection Setup Response message to the eNB, indicating a successful reception of the D2D Connection Setup message. The device handshake/discovery procedure may subsequently begin.

The RRC D2D HS Setup messages 402 and 404 may contain transmission/reception parameters associated with a device handshake. Device handshake transmission/reception parameters may include: transmission patterns, transmit point IDs, device-to-device radio network temporary identity (DD-RNTI) etc. The transmission patterns may be indicated by an index of a transmission pattern. For example, a set of transmission patterns may be defined, such as in a standards document, with corresponding indices. Alternatively specific parameters which may be used to generate the transmission pattern/sequence may be indicated. This message may also include an indication of whether the uplink (UL) radio resources or downlink (DL) radio resources are assigned for handshake procedure and the subsequent data transmission over the direct inter-device communication link.

The eNB may indicate minimum and maximum transmit power levels P mn and P mx to the UEs as part of the RRC message, for example, in the RRC D2D HS Setup messages 402 and 404 , or in an RRC D2D Connection Setup message. The eNB may set the minimum and maximum transmit power levels based, e.g., on the vicinity of the UEs participating in the inter-device communication and the link loss profile in that specific area.

A quality test procedure 426 may then be performed by one or more of UE 0 , UE 1 , and the eNB over the direct communication link. The quality test procedure may include a number of message exchanges between UE 1 and UE 0 over the direct inter-device communication link between UE 1 and UE 0 , e.g., 414 - 420 , to set up an appropriate transmit power level for UE 1 and UE 0 . The eNB may allocate/ grant radio resources for UE 1 and UE 0 to transmit over the inter-device communication link in PDCCH messages 410 and 412 . The Cyclic Redundancy Check (CRC) of these PDCCH messages are scrambled by the DD-RNTI. The radio resources over which a specific UE transmits the transmission patterns are indicated by tagging those resources with the UE's TP ID. The time between recurring resource grants for the same UE are decided by the expected time for UE to detect the transmission pattern and respond. To differentiate from the regular data transmission over the inter-device communication link, the PDCCH message may include a bit to indicate that the handshake transmission pattern will be transmitted over the inter-device communication link.

As illustrated in FIG. 4 , to start the power adjustment procedure, UE 0 may send a sequence s 0 to UE 1 over the assigned inter-device link resources at 414 . The transmit power level of UE 0 P UE0 is between the minimum and maximum transmit power levels, i.e., P mn ≤P UE0 ≤P mx . In one approach, the transmit power is set as P mn or close to P mn at the start of the handshake procedure. UE 1 may process the received signal, for example, by cross correlating the received signal with the sequence s 0 and comparing the correlation value with a quality indicator.

If the received signal quality at UE 1 is acceptable, UE 1 may then transmit a sequence s 1 at a transmit power level, P UE1 , P mn ≤P UE1 ≤P mx , at 416 . In one approach, the transmit power is set as P mn or close to P mn at the start of the handshake procedure. Otherwise, UE 1 may transmit sequence s 0 at the transmit power level P UE1 at 416 . Correspondingly, if UE 0 receives sequence s 0 at 416 , the transmit power level of UE 0 is increased to P UE0 =P UE0 +Δ TP for the subsequent transmission at 418 and future transmissions to UE 1 . Δ TP represents an incremental value for the transmit power level and may be called a transmit power step. If the received signal quality of s 0 is acceptable, UE 0 transmits sequence s 1 in the next transmission 418 at the increased power level. If the received signal quality of s 0 is not acceptable, UE 0 transmits sequence s 0 in the next transmission 418 at the increased power level.

On the other hand, if UE 0 receives sequence s 1 at 416 , the transmit power level of UE 0 may be fixed at P UE0 for the subsequent transmission 418 and future transmissions to UE 1 . If the received signal quality of s 0 is acceptable, UE 0 transmits sequence s 1 in the next transmission 418 at the fixed power level P UE0 . If the received signal quality of s 0 is not acceptable, UE 0 transmits sequence s 0 in the next transmission 418 at the fixed power level P UE0 . If neither sequence s 0 nor s 1 is detected from the received signal, UE 0 may indicate to the eNB that the device handshake/discovery procedure is unsuccessful.

UE 0 and UE 1 may repeat steps 414 - 418 until an acceptable received signal quality is reached at both UE 0 and UE 1 . At the end of a successful handshake/discovery procedure, UE 0 and UE 1 may send RRC D2D HS Response messages 422 and 424 to the eNB, including their respective transmit power levels and indicating to the eNB that the device discovery/handshake procedure is successful. A Channel Quality Indicator (CQI) of the direct communication link may also be measured by UE 0 and UE 1 and reported to the eNB such that the eNB may assign an appropriate modulation and coding scheme (MCS) for future data exchanges over the inter-device communication link. It is to be understood that similar procedures may be applied to a scenario where more than 2 UEs are involved in a group inter-device communication, such as interactive gaming, conference calling, etc. The above described transmit power level optimization can be modified with the introduction of another transmit pattern/sequence s 2 . This is useful if the UEs are allowed to select any initial transmit power level between P mn and P mx . In this case a third transmit pattern may be used to indicate a decrease the transmit power level during the next transmission.

FIG. 5 illustrates a flow chart 500 of an example method for adjusting a device transmit power level of UE 0 for inter-device communication. As shown in FIG. 5 , UE 0 may start transmitting sequence s 0 at power level P UE0 over the inter-device communication link at 502 during the device handshake/discovery procedure. Next, UE 0 may receive a transmission from another UE over the inter-device communication link. UE 0 then correlates the received signal with s 0 or s 1 at 504 . For example, UE 0 may calculate the following metric: Γ i =| r(k),s* i *(k) | 2 /| s i (k),s* i (k) | 2 for i=0,1, where x, y indicates the inner product of x and y and |a| indicates the magnitude of a. r(k) and s i (k) represent the kth element or symbol of the received signal and the ith transmitted pattern or sequence. The superscript ‘*’ represents the complex conjugate operation. Alternatively, the received signal r(k) may be passed through a filter matched to the transmit patterns s 0 and s 1 . UE 0 checks whether the received signal is sequence s 1 at 506 . For example, UE 0 may determine that s 1 is transmitted if Γ 1 >Γ 0 and Γ 1 >η, where η is a measure of the thermal noise power of the UE receiver. η may further include other interference power. If sequence s 1 is received at 506 , UE 0 may further check whether the received signal quality is acceptable at 508 . This may be done, for example, by checking if Γ 1 is greater than β, a CQI threshold as specified by the serving cell. If the received signal quality is acceptable, i.e. Γ 1 >β, UE 0 may transmit sequence s 1 at power level P UE0 over the inter-device communication link at 510 . UE 0 may also indicate the transmit power level P UE0 and a successful device handshake/discovery process to the serving eNB at 512 . If the received signal quality is not acceptable, UE 0 may transmit sequence s 0 at power level P UE0 at 514 and return to 504 of the flow chart.

If sequence s 1 is not received at 506 , UE 0 may proceed to check whether sequence s 0 is received at 516 . For example, UE 0 determines that s 0 is transmitted if Γ 0 >Γ 1 and Γ 0 >η. If sequence s 0 is received, UE 0 may further check whether the received signal quality is acceptable at 518 . If the received signal quality is acceptable, i.e. Γ 0 >β, UE 0 may transmit sequence s 1 at an increased power level P UE0 =P UE0 +Δ TP over the inter-device communication link at 520 . If the received signal quality is not acceptable, UE 0 may transmit sequence s 0 at the increased power level P UE0 =P UE0 +Δ TP at 522 and return to 504 of the flow chart.

If sequence s 0 is not received at 516 , UE 0 may set the transmit power level to P UE0 =P UE0 +Δ TP at 524 for the next transmission over the inter-device communication link. For example, UE 0 determines that neither s 0 or s 1 are transmitted if Γ 0 ≤η+ϵ and Γ 1 ≤η+ϵ, where ϵ is a positive number and specified by the UE receiver. UE 0 may further check whether the increased transmit power level P UE0 is less than the maximum transmit power level P mx at 526 . If the increased transmit power level P UE0 is less than the maximum transmit power level, UE 0 may transmit sequence s 0 at the next transmit instant at 528 and return to 504 of the flow chart. Otherwise, if the increased transmit power level P UE0 is not less than the maximum transmit power level, UE 0 may indicate a device handshake/discovery failure to the serving eNB at 530 . The above described transmit power level optimization can be modified with the introduction of another transmit pattern/sequence s 2 . This may be useful, e.g., if the UEs are allowed to select any initial transmit power level between P mn and P mx . In this case the third transmit pattern s 2 is used to indicate a decrease the transmit power level during the next transmission.

FIG. 6 illustrates a flow diagram of another example method for adjusting a device transmit power for inter-device communication. The serving eNB may initiate the D2D Handshake procedure during the direct inter-device call set up or anytime during an ongoing direct communication between the UEs. During the initial call set up the serving eNB may initiate the handshake procedure multiple times to decide the direct inter-device communication link quality. For example the HS procedure may be initiated two times, once using DL radio resources and another time using UL resources. Based on the CQI feedback either UL or DL radio resources are used to enable the direct inter-device communication link. Similarly, specific radio resources over the DL/UL link may be selected based on the CQI feedback. This can be performed by initiating the HS procedure over multiple frequency segments of radio resources. For example HS procedure can be initiated over different set of resource blocks in an LTE system. As illustrated in FIG. 6 , at 602 , the eNB may initiate HS procedure using the DL radio resources. At 604 - 606 , the UEs, UE 0 and UE 1 send the CQI based on the received signal from UE 1 and UE 0 respectively. At 608 , the eNB may initiate HS procedure using the UL radio resources. At 610 - 612 , the UEs, UE 0 and UE 1 send the CQI based on the received signal from UE 1 and UE 0 respectively. Based on the received CQIs at 604 - 606 and 610 - 612 , appropriate radio resources are selected for the inter-device communication link and indicated to one or both UEs at 614 in an RRC D2D Connection setup message.

In some implementations, to facilitate the device discovery process, the UE that intends to get involved in the direct-link communication may start periodically broadcast a “beacon” signal to identify itself. The beacon signal could be transmitted over the pre-defined resource or UE specific resource. In one example, if the beacon signal is transmitted over the pre-defined resource, the UE may use orthogonal code sequence for the beacon signal in order to identify itself. In another example, if the beacon signal is transmitted over the UE specific resource, the UE may share the same code sequence. The resource may be directly assigned by the eNB or linked directly with the UE ID. The beacon signal carries at least the UE ID information and is transmitted periodically on pre-determined resources. Other UEs that are capable of conducting inter-device communications may detect the “beacon” signal. The periodic beacon signal may be transmitted/detected only when the UE intends to get involved in the direct-link communication. For example, when UE 0 intends to participate in direct-link communication and starts to broadcast a beacon signal, surrounding UEs may detect the beacon signal and consider UE 0 as a potential direct-link communication candidate if the beacon signal strength is above a pre-defined threshold value. Then one or more surrounding UEs may initiate a direct-link communication with UE 0 . The transmit power of this beacon signal may be set by the network such that transmitted beacon signals in a cell do not cause excessive interference within the network. For example, the power level of the beacon signal can be set to be very low, e.g. 10-15 dBm, when the user density within a cell is high.

The systems and methods described above may be implemented by any hardware, software or a combination of hardware and software having the above described functions. The software code, either in its entirety or a part thereof, may be stored in a computer readable memory.

While several implementations have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be implemented in many other specific forms without departing from the scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. Method steps may be implemented in an order that differs from that presented herein.

Also, techniques, systems, subsystems and methods described and illustrated in the various implementations as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

While the above detailed description has shown, described, and pointed out the fundamental novel features of the disclosure as applied to various implementations, it will be understood that various omissions and substitutions and changes in the form and details of the system illustrated may be made by those skilled in the art, without departing from the intent of the disclosure. Although certain illustrated examples in this disclosure may show only two UEs, the described systems and methods for the inter-device communications can be applied to more than two UEs without departing from the scope of the present disclosure.