Systems, methods, and devices for device-to-device discovery

A user equipment (UE) includes a reference signal component, a guard period component, and a transmission component. The reference signal component is configured to randomly select a sequence for a reference signal for transmission in an open device-to-device discovery packet. The guard period component is configured to determine a first symbol signal for transmission during a first symbol of the device-to-device discovery packet. The first symbol comprises a partially punctured symbol. The transmission component is configured to transmit the device-to-device discovery packet. The device-to-device discovery packet includes the first symbol having the partially punctured symbol and a reference signal based on the randomly selected sequence.

TECHNICAL FIELD

The present disclosure relates to device-to-device communication.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Wireless mobile communication technology uses various standards and protocols to transmit data between a base station and a wireless communication device. Wireless communication system standards and protocols can include, for example, the 3rd Generation Partnership Project (3GPP) long term evolution (LTE); the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard, which is commonly known to industry groups as worldwide interoperability for microwave access (WiMAX); and the IEEE 802.11 standard, which is commonly known to industry groups as Wi-Fi. In a 3GPP radio access network (RAN) according to LTE, the base station is termed Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Node B (also commonly denoted as evolved Node B, eNodeB, or eNB). It may communicate with a wireless communication device, known as user equipment (UE). Although the present disclosure is presented with terminology and examples generally directed towards 3GPP systems and standards, the teaching disclosed herein may be applied to any type of wireless network or communication standard.

FIG. 1is a schematic diagram illustrating a communication system100that includes a plurality of UEs102in communication with network infrastructure104. The network infrastructure104includes an evolved packet core (EPC)106and an E-UTRAN108. The EPC106includes mobility management entities (MME) and serving gateways (S-GW)112that communicate with eNodeBs110in the E-UTRAN108over an S1 interface. The S1 interface as defined by 3GPP supports a many-to-many relation between EPC106and eNodeBs110. For example, different operators may simultaneously operate the same eNodeB110(this is also known as “network sharing”). The E-UTRAN108is a packet switched 3GPP RAN for LTE (i.e., 3.9G) and LTE-Advanced (i.e., 4G) that was first introduced in 3GPP Release 8 and continues to evolve. In the E-UTRAN108the eNodeBs110are more intelligent than legacy Node Bs of a universal terrestrial radio access network (UTRAN) used in universal mobile telecommunication systems (UMTS or 3G). For example, almost all the radio network controller (RNC) functionality has been moved to the eNodeB rather than being in a separate RNC. In LTE, eNodeBs110are connected with each other by means of an X2 interface that allows the eNodeBs110to forward or share information.

The UEs102may include a radio that is configured to transmit and receive signals in a licensed wireless spectrum corresponding to the eNodeBs110. The UEs102are in communication with an eNodeB110using a Uu air interface on a licensed cellular spectrum. The UEs102and eNodeBs110may communicate control data and/or user data with each other. A downlink (DL) transmission in an LTE network can be defined as a communication from the eNodeB110to the UE102, and an uplink (UL) transmission can be defined as a communication from the UE102to the eNodeB110.

In addition to DL and UL transmissions over the Uu interface, the UEs102are also shown communicating directly with each other over a Ud air interface. Direct communication between devices is commonly known as proximity services (ProSe), device-to-device (D2D) communication, or peer-to-peer (P2P) communication. In D2D, a UE102is able to communicate directly with another UE102without routing communications via an eNodeB110or the core network (e.g., EPC106), as illustrated by the Ud D2D interface inFIG. 1. D2D is a powerful technique for increasing network throughput by enabling direct communications between mobile stations rather than using network infrastructure104, and has a wide variety of applications. For example, D2D has been proposed for local social networks, content sharing, location-based marketing, service advertisements, public safety networks, mobile-to-mobile applications, etc. D2D communications are of interest due to their ability to reduce load on a core network (such as the EPC106) or a radio access network (such as the E-UTRAN108), increase data rates due to direct and short communication paths, provide public safety communication paths, and provide other functionality. In some embodiments, the UEs may be connected to different eNodeBs or to completely different networks operated by different mobile network operators (MNOs).

There are various alternatives to realize such a direct communication path between mobile devices. In one embodiment, the D2D air interface Ud could be realized by some type of short-range technology, such as Bluetooth or Wi-Fi, or by reusing licensed LTE spectrum, such as a UL spectrum. Furthermore, D2D communications can be generally divided into two parts. The first part is device discovery, whereby UEs102are able to determine that they are within range and/or available for D2D communication. Proximity detection may be assisted by network infrastructure104, may be performed at least partially by the UEs102, or may be performed largely independent of the network infrastructure104. The second part is direct communication, or D2D communication, between UEs102, which includes a process to establish a D2D session between UEs102as well as the actual communication of user or application data. D2D communication may or may not be under continuous control of an MNO. For example, the UEs102may not need to have an active connection with an eNodeB110in order to take part in D2D communications.

For D2D discovery, there are generally two different approaches: restricted D2D discovery (also known as closed D2D discovery) and open D2D discovery (also known as promiscuous D2D discovery). Restricted D2D discovery applies to use cases wherein a discoverable device may be discovered only by a select set of ProSe enabled discovering devices. For example, only pre-identified or selected devices may be allowed to connect, such as devices identified or selected by the network, a P2P server, an application, or a user. Thus, for this use case, a discovering device would be assumed to know, in advance, the ProSe enabled device it wishes to discover in its proximity, including any corresponding identifiers.

On the other hand, open device discovery considers use cases wherein a discoverable device may want itself to be discovered by any or all ProSe enabled devices in its proximity. From the perspective of the discovering device, open device discovery implies that a discovering device may not be assumed to be aware of the identity of other ProSe enabled devices prior to discovery. Consequently, the device discovery mechanism for open discovery may aim towards discovering as many ProSe enabled devices in its proximity as possible.

In certain situations, such as for open D2D discovery using licensed resources, an eNodeB has limited control of the discovery process among UEs. In particular, an eNodeB may periodically allocate certain discovery resources in the form of D2D discovery regions (e.g., time/frequency resources such as resource blocks or subframes) for UEs102to transmit the discovery information. The discovery information may be in the form of a discovery sequence or discovery packet with payload information.

In this application, applicants disclose systems, methods, and devices for D2D discovery and communication. In one embodiment, a UE includes a reference signal component, a guard period component, and a transmission component. The reference signal component is configured to randomly select a sequence for a reference signal for transmission in a device-to-device discovery packet. The guard period component is configured to determine a first symbol signal for transmission during a first symbol of the device-to-device discovery packet. The first symbol may include a partially punctured symbol. The transmission component is configured to transmit the device-to-device discovery packet that includes the partially punctured symbol and a reference signal based on the randomly selected sequence.

The present disclosure also discusses locations of reference signals within the discovery packet, such as an orthogonal frequency division multiplexing (OFDM) discovery packet. As used herein, the term “discovery packet” is given to mean a packet of information comprising a preamble or header and payload data. The term discovery packet is to be broadly construed as referring not only to a logical data structure but also to a logical resource structure. For example, the term discovery packet, as used herein, encompasses not only payload data but also physical layer signaling (such as reference signals) and control data.

As background, a discussion of resource structure may be helpful.FIG. 2illustrates one embodiment of a basic structure for a time-frequency resource as defined in LTE. The resource includes a plurality of radio frames with a length of about 10 milliseconds (ms). Each radio frame includes a grid of subframes, each with a length of about 1 ms. Each subframe includes a plurality of subcarriers and symbols which form resource elements. In one embodiment, a subframe includes two slots, or resource blocks, which each span a plurality of symbols (seven time periods) and subcarriers (e.g., twelve frequency bands). In a normal cyclic prefix case, each resource block includes seven symbols, as depicted.

The above embodiments are given by way of example only. Further details and example embodiments will be discussed below.

FIG. 3is a schematic block diagram illustrating one embodiment of a UE102configured for D2D discovery. The UE102includes a communication mode component302, a receiver component304, a scheduling component306, a reference signal component308, a guard period component310, a transmission component312, a discovery information component314, a blind sequence detection component316, and a channel component318. The components302-318are shown by way of example and may not all be included in all embodiments. In some embodiments, only one or any combination of two or more of the components302-318may be included.

The communication mode component302controls a communication mode of one or more radios of the UE102. In one embodiment, the UE102may include one or more two-way radios and/or antennas for receiving and uploading data to the network infrastructure104. In one embodiment, the same radio or antenna may be used for both signal transmission and reception, but generally not at the same time. The communication mode component302is configured to switch the respective radios from a reception mode to a transmission mode and from a transmission mode to a reception mode, as needed. The process of ramping up or ramping down power in a radio or on an antenna to place it in a desired mode takes some time and thus there is often a need for a guard period or puncturing of a resource structure to allow for the switch. According to agreement by the LTE radio layer 1 (RAN1) working group, TS×624 is assumed for both transmission mode to reception mode switching and reception mode to transmission mode switching. This amount of time is meant to allow for communication mode switching times as well as propagation delays for receiving transmitted signals. Ts is the basic time unit with

TS=1(15000×2048)⁢seconds
so that TS×624≈20 microseconds (μs). Thus, in some situations, a guard period may be included to allow for the switch in communication modes and propagation delays. Further discussion of guard periods will take place in relation to the guard period component310.

The receiver component304is configured to receive information or signals received by an antenna or radio of the UE102. For example, the receiver component304may receive DL signals from an eNodeB110or may receive signals transmitted by a peer UE when a corresponding radio is in a reception mode. In one embodiment, the receive component304may provide received information to other components302,306-318as appropriate.

The scheduling component306is configured to receive a message scheduling usage of one or more wireless resources. In one embodiment, the scheduling component306may receive a control message from an eNodeB110indicating that a specific portion of licensed wireless resources is to be used for a specific purpose. For example, the scheduling component306may receive a message from 3GPP LTE network infrastructure104allocating wireless resources licensed by an MNO for device-to-device discovery. The scheduling component306may determine whether the UE102needs to participate in device-to-device discovery. If the scheduling component306determines a need to establish a D2D session, the scheduling component306may schedule the allocated resources for transmitting discovery information or listening for discovery information transmitted by a peer UE.

The reference signal component308may determine or generate a reference signal for transmission. Reference signals are often included in wireless transmission to allow receiving devices to estimate the channel, synchronize in time, synchronize in frequency, or the like. Example reference signals in LTE include sounding reference signals (SRS) and demodulation reference signals (DM-RS). In some cases, reference signals include signals based on a basic sequence and modified by a cyclic shift or orthogonal cover code to reduce interference and allow a receiving device to distinguish the transmission from transmissions of other devices. Generally, a sequence and modifications (e.g., cyclic shift or orthogonal cover code) are preconfigured or predefined (e.g., by a communication standard or by previous physical layer or higher layer signaling) such that a UE102knows what reference signal sequence to use, and devices or systems interested in receiving transmissions know what to expect.

However, in some situations, such as for open discovery, devices may not be listening for a specific UE or reference signal sequence. Because the transmitting UE and the receiving UE may not even be aware of each other, they may not be able to determine what sequence will be used for a reference signal. In one embodiment, if no specific sequence is indicated, the reference signal component308randomly selects a sequence for transmitting a D2D discovery transmission. For example, the reference signal component308may randomly select a cyclic shift or an index for an orthogonal cover code and allow a receiving UE to blindly determine what cyclic shift or orthogonal cover code was used. In one embodiment, a basic sequence may be configured by network infrastructure104or by a protocol, and the reference signal component308may randomly select a modification to the basic sequence to transmit. In one embodiment, the reference signal component308may randomly select a sequence for a reference signal for transmission during a resource allocated by an eNodeB110for device-to-device discovery. Further details of reference signals, sequence selection, and reference signal generation will be discussed in relation to the blind sequence detection component316and later figures.

The guard period component310is configured to determine a guard period for a D2D discovery period. For example, the guard period component310may determine a guard period for a first symbol of an OFDM resource allocated for discovery. In one embodiment, resources allocated for D2D discovery may be located following another resource block or frame where a UE needs to switch a communication mode. For example, the UE102may be receiving a DL communication from an eNodeB110in the previous subframe or frame and may need to ramp up power on the same radio to transmit a discovery packet during the resource allocated for D2D discovery. Similarly, the UE102may be transmitting a UL communication in the previous sub frame or frame and may need to ramp down power on the same radio to listen for a discovery packet during the resource allocated for D2D discovery.

In one embodiment, the guard period component310is configured to determine a first symbol signal for transmission during a first symbol of the device-to-device discovery packet. The guard period component310may receive an indication of a reference signal and/or data to be transmitted during the first symbol and generate the first signal or determine a structure of the first signal within the first symbol. In one embodiment, the guard period component310determines a signal for a partially punctured first symbol. The term punctured is given to mean that the basic resource structure is modified to prohibit or limit a requirement to transmit or receive data during the punctured portion of the resource. For example, even if a signal is transmitted during a punctured portion, a receiving device may be able to receive the same data during a non-punctured portion of the resource structure. On the other hand, transmission or reception during the punctured portion may be prohibited.

In one embodiment, the guard period component310determines the signal for the first symbol by determining or generating a repeating signal for the first symbol. For example, the signal for the first symbol may include a repeating reference signal or a repeating data signal. The reference signal or data may be repeated twice within the first symbol to allow transmitting or receiving devices to transmit or receive the second transmission. For example, if a UE102was transmitting in a resource block immediately preceding a resource allocated for discovery, the UE102may finish transmission, and the communication mode component302may switch the corresponding radio to a reception mode. However, due to the delay in switching, the UE102may not be able to receive a first portion of a signal transmitted in the first symbol. By the time the second iteration or repetition of the signal begins, the UE102is ready to receive the signal, and no data or information is lost because the missed portion is repeated. In one embodiment, the signal may be repeated two, three, or more times in the first symbol to allow for devices to switch, if needed. In one embodiment, the guard period component310may drop a last repetition of a signal and move the signal backwards by the length of the dropped repetition to provide for a punctured first symbol (e.g., seeFIGS. 4 and 5). For example, a cyclic prefix (CP) and first repetition block may be moved backwards in time, and a last repetition may be dropped from the first symbol.

In one embodiment, the guard period component310generates a guard period by determining a signal for the first symbol that does not include power or information in a first portion of the first symbol but has power or information during a second portion of the first symbol. For example, the first portion may correspond to an amount of time that allows for communication mode switching, such as TS×624 as discussed above. In one embodiment, the first portion has a length of about 20 ms or more. In one embodiment, the first portion has a length corresponding to about one-third of a time length of the first symbol. For example, the first symbol may have a length of about 1 ms divided by 14 (for 14 symbols), or

1⁢⁢ms14⁢⁢symbols≈71⁢⁢μ⁢⁢s.
Thus, the first portion may have a length of

71⁢⁢μ⁢⁢s3≈20⁢⁢μs.
In one embodiment, the first portion has a length corresponding to about one-half of a time length of the first symbol. Thus, the first portion may have a length of

71⁢⁢μ⁢⁢s2≈35.5⁢⁢μs.
In one embodiment, the guard period component310generates a guard period based on interleaved frequency division multiple access (IFDMA).

In one embodiment, the guard period component310may also create a guard period in a last symbol of discovery to allow for timing changes or communication mode switches at an end of D2D discovery.

The transmission component312is configured to transmit signals using a radio or antenna of the UE102. In one embodiment, the transmission component312transmits a discovery packet based on information received or provided by other components of the UE102. For example, the transmission component312may transmit a discovery packet during a resource scheduled by the scheduling component306. In one embodiment, the transmission component312transmits reference signals determined by the reference signal component308within a discovery packet. In one embodiment, the transmission component312receives data or signal information, and maps the data or signals to appropriate blocks in a resource structure based on a physical layer protocol. For example, the transmission component312may transmit a discovery packet with reference signals, data, and/or unused symbols as required by the LTE physical layer or as otherwise specified herein.

In one embodiment, the transmission component312is configured to transmit a D2D discovery packet with a guard period at the beginning of the transmission. For example, the transmission component312may transmit a D2D discovery packet in an OFDM structure, such as in an OFDM resource block or subframe, with a partially punctured first symbol. In one embodiment, the transmission component312transmits the first symbol of the discovery packet without power on one or more of the subcarriers during the first symbol. For example, a fraction of the plurality of subcarriers may be unused during the whole first symbol. In one embodiment, the fraction of unused subcarriers may be calculated by

RPF-1RPF,
where RPF is the repetition factor that determines how many times a reference signal or data signal is repeated in the first symbol.

In one embodiment, the transmission component312transmits a reference signal with a discovery packet. For example, the transmission component312may transmit the reference signal within an OFDM resource block comprising at least a portion of discovery information for the UE102. In one embodiment, the transmission component312transmits the reference signal during the first symbol of the allocated discovery resource. For example, the transmission component312may transmit a reference signal based on a randomly selected sequence selected by the reference signal component308during the first symbol. In one embodiment, the transmission component312transmits the reference signals during a first symbol of each resource block of the resources allocated for D2D discovery, such as the first and eighth symbols of a subframe. In one embodiment, the transmission component312transmits the reference signals during a fourth symbol of each resource block of the resources allocated for D2D discovery, such as the fourth and eleventh symbols of a subframe. In one embodiment, the transmission component312transmits a reference signal and discovery data as part of an open discovery packet.

The discovery information component314is configured to obtain D2D discovery information. For example, the discovery information component314may receive a discovery packet for open D2D discovery transmitted by a peer UE during a resource allocated for D2D discovery. In one embodiment, the discovery information includes an identifier for the peer UE that transmitted the discovery information. The identifier may be used by the UE102to transmit a request to establish a D2D session with the corresponding UE. In one embodiment, the discovery information includes a reference signal that was generated using a reference signal sequence that is unknown to the receiving UE102. For example, the transmitting UE may have transmitted the reference signal based on a randomly selected sequence, as discussed above in relation to the reference signal component308.

The blind sequence detection component316is configured to determine an unknown sequence for a received reference signal. For example, the blind sequence detection component316may determine a cyclic shift or orthogonal cover code used to generate a reference signal received in a discovery packet. In one embodiment, the blind sequence detection component316determines the unknown sequence by comparing the received reference signal with reference signals generating known cyclic shifts or orthogonal cover codes. For example, a basic sequence for the discovery packet may be known, but the specific cyclic shift or orthogonal cover code may be unknown. In one embodiment, if UL DM-RSs are received as the reference signal for D2D discovery, a DM-RS blind detection algorithm which targets to find a candidate sequence with maximum correlation energy to the actual received reference signal can be employed to determine the cyclic shift of the DM-RS sequence of the transmit UEs. In one embodiment, the blind sequence detection component316may determine the unknown sequence by attempting to interpret the reference signal using one or more potential cyclic shifts or orthogonal cover codes for a known basic sequence. For example, the blind sequence detection component316may attempt to interpret using a first potential cyclic shift and, if unsuccessful, try a second potential cyclic shift, and so on until the correct cyclic shift is attempted. Similar attempts may be performed with potential orthogonal cover codes on a known basic sequence.

The channel component318estimates a channel between the UE102and a source UE based on the reference signal with the unknown sequence. In one embodiment, the discovery information component314receives a DM-RS having an unknown randomly selected DM-RS sequence. From the perspective of a receiving UE, the blind sequence detection component316performs blind detection of the DM-RS sequence, and the channel component318performs estimation and synchronization to ensure an appropriate channel estimation, timing, and frequency offset compensation for the source UE.

FIGS. 4 and 5illustrate example guard periods for a first symbol of an OFDM symbol. Specifically,FIGS. 4 and 5illustrate guard period generation based on IFDMA signal structure, which may be performed by the guard period component310.FIG. 4illustrates puncturing of a first half of the first symbol. Specifically, the first symbol uses an IFDMA signal structure with an RPF of 2. In this case, data or reference symbols can be mapped into every even subcarrier in the frequency domain, creating a comb-like spectrum. As illustrated, this design pattern results in two repeated blocks in the first OFDM symbol402in the time domain. By puncturing the second repetition block and subsequently shifting the cyclic prefix (CP) and first repetition block, as shown in the punctured first symbol404, an approximately 33 μs guard period in the first OFDM symbol can be generated. Note that this proposed guard period generation can be applied for both reference signals and data symbols.

In the case where a DM-RS is transmitted during the first symbol, the discovery DM-RS sequence may reuse the existing Zadoff-Chu (ZC) sequence. In one embodiment, a different sequence can also be considered for the discovery DM-RS sequence design. An example of preamble generation for the first OFDM symbol is described as follows. The reference signal sequence or modulated symbols in the first symbol may be multiplied with an amplitude scaling factor βD2Din order to conform to a transmit power PD2Dand may be mapped in sequence starting with rD2D(0) to resource elements (k, 0) according to:

a2⁢k′+k0,0={βD⁢⁢2⁢D⁢rD⁢⁢2⁢D⁡(k′),k′=0,1,K,MD⁢⁢2⁢DRS⁢/⁢2-10,otherwiseEq.⁢(1)
where k0is the frequency-domain starting position of the discovery resource block, MD2DRSis the length of the reference signal sequence, and MD2DRS=mND2DRB. InFIG. 4, ND2DRB=12 and m is within the range 1≦m≦ND2DRB,UL. The D2D discovery reference signal sequence in the first OFDM symbol rD2D(n)=ru,v(αD2D)(n) may be used as defined by 3GPP TS 36.211, Section 5.5.1, where u is the sequence-group number defined in 3GPP TS 36.211, Section 5.5.1.3, and v is the base sequence number defined in 3GPP TS 36.21, Section 5.5.1.4. The cyclic shift αD2Dof the discovery reference signal in the first OFDM symbol is given as:

αD⁢⁢2⁢D=2⁢π⁢nD⁢⁢2⁢DcsND⁢⁢2⁢DRS(Eq.⁢2)
where ND2DRSis the number of cyclic shifts for D2D discovery and may have the value 6, 8, or 12. nD2Dcs={0, 1, 2, L, ND2DRS−1} is the cyclic shift index. For open D2D discovery, ProSe enabled UEs may randomly select the cyclic shift index when transmitting the discovery packet, as discussed above. For restricted ProSe discovery, nD2Dcsmay be configured by higher-layer signaling, such as by an application layer or radio resource control (RRC) layer.

Note that when discovery packet transmission occupies one resource block (i.e., MD2DRS=12), a new base sequence may be used. In general, the new base sequence will have constant modulus in the frequency domain, low peak-to-average power ratio (PAPR), low memory/complexity requirements, and good cross-correlation properties. An example of a base sequence with six phase values which may be used is given below.

InFIG. 5, an IFDMA signal structure with an RPF of 3 is illustrated. In the frequency domain, either data or reference symbols can be mapped onto every third subcarrier. As illustrated, this would create three repeated blocks in the first OFDM symbol502in the time domain. By puncturing the repetition block #3 and shifting the CP and first two repetition blocks, as shown in the punctured first symbol504, an approximately 22 μs guard period can be generated.

An example of preamble generation for the first OFDM symbol based on RPF 3 is described as follows. The reference signal sequence or modulated symbols may be multiplied with the amplitude scaling factor βD2Din order to conform to a transmit power PD2Dand may be mapped in sequence starting with rD2D(0) to resource elements (k, 0) according to:

a3⁢k′+k0,0={βD⁢⁢2⁢D⁢rD⁢⁢2⁢D⁡(k′),k′=0,1,K,MD⁢⁢2⁢DRS⁢/⁢3-10,otherwise(Eq.⁢5)
where k0is the frequency-domain starting position of the discovery resource block, MD2DRSis the length of the reference signal sequence, and MD2DRS=mND2DRB. InFIG. 5, ND2DRB=12 and m is within the range 1≦m≦ND2DRB,UL.

It is worth mentioning that the structures of bothFIG. 4andFIG. 5can be easily extended to support public safety-specific use cases in partial and outside-network coverage scenarios. For instance, the last OFDM symbol may be punctured in the same way as the first OFDM symbol in order to accommodate an even larger synchronization error.

Turning now toFIGS. 6-13, physical layer structures for D2D discovery signals are proposed. For D2D discovery, a certain number of primary resource block (PRB) pairs (i.e., subframes) mapped in a certain way (frequency first, time first, or following a mixed mapping) to time-frequency resources can be used to carry the discovery packet. Let us denote Nf×Ntas the time-frequency resources, where Nfis the number of resource blocks in the frequency domain and Ntis the number of slots or subframes in the time domain. For instance, for a 2×1 frequency domain resource allocation scheme, each discovery packet transmission occupies24subcarriers within one subframe. For a 1×2 time-domain resource allocation scheme, each discovery packet transmission spans two subframes and occupies12subcarriers in each subframe. Note that when the discovery packet transmission spans more than one subframe, guard periods in the first OFDM symbol of the second and subsequent subframes may not be needed, which would provide a lower coding rate and thereby better link level discovery performance.FIGS. 6-13cover four generally different physical layer structures for D2D discovery signal designs.

FIGS. 6 and 7illustrate a first example option for D2D discovery signal design. In the first example option, a DM-RS is located in the first OFDM symbol for each slot (i.e., resource block), which can be constructed based on the UL DM-RS for physical uplink shared channel (PUSCH) transmission. More specifically, for restricted ProSe discovery, the discovery DM-RS can be generated according to 3GPP TS 36.211, Section 5.5.2.1. For open ProSe discovery, the discovery DM-RS can be generated as follows.

As mentioned in the proposed guard period generation procedure, the length of a DM-RS sequence would be reduced by half (in the case of RPF=2) or ⅔ (in the case of RPF=3) for the first OFDM symbol. Furthermore, data symbols may be generated by utilizing either single carrier FDMA (SC-FDMA) or OFDMA transmission schemes.

FIGS. 6 and 7illustrate discovery signal structures600and700, according to the first example option above, with Nf×1 and 1×Nftime-frequency resource mapping, respectively. A guard period in the first OFDM symbols602and702is shown based on the guard period generation with half of the subcarriers allocated for the reference signal, as discussed above with an RPF of 2. The first OFDM symbols604and704of the second slot (slot 1) also include a reference signal, but are not punctured. Note that in the examples ofFIGS. 6-13, a guard period generation procedure with half of the subcarriers allocated for reference or data symbols is assumed unless otherwise stated. In addition, although the examples shown are based on the normal CP, D2D discovery signal designs can be easily generated for the extended CP case.

Turning toFIGS. 8 and 9, a second example option for D2D discovery signal design is discussed. In the second example option, the discovery DM-RS occupies the centered OFDM symbol for each slot as well as the first OFDM symbol of the first slot (slot 0). The discovery DM-RS allocated for the centered OFDM symbol can be generated according to 3GPP TS 36.211, Section 5.5.2.1. For open ProSe discovery, the discovery DM-RS can be generated as follows.

As mentioned in the proposed guard period generation procedure, the length of a DM-RS sequence would be reduced by half (in the case of RPF=2) or two-thirds (in the case of RPF=3) for the first OFDM symbol. Furthermore, data symbols may be generated by utilizing either SC-FDMA or OFDMA transmission schemes.

FIGS. 8 and 9illustrate discovery signal structures800and900, according to the second example option above, with Nf×1 and 1×Nftime-frequency resource mapping, respectively. A guard period in the first OFDM symbols802and902is shown based on the guard period generation with half of the subcarriers allocated for the reference signal, as discussed above with an RPF of 2. The centered symbols804,904and806,906are shown with reference signals, but are not punctured.

Turning toFIGS. 10 and 11, discovery signal structures1000and1100represent a third example option for D2D discovery signal design. In the third example option, the discovery DM-RS occupies the centered OFDM symbols1004,1104and1006,1106for each slot. The discovery DM-RS generation for the centered OFDM symbol is the same as discussed with reference toFIGS. 8 and 9. In addition, for the first OFDM symbols1002and1102, data signals are mapped into every even subcarrier to generate guard periods within the first symbol. Furthermore, the first data symbol is generated based on an OFDMA transmission scheme.FIGS. 10 and 11illustrate the third example option discovery signal design with Nf×1 and 1×Nftime-frequency resource mapping, respectively.

Turning toFIGS. 12 and 13, a fourth example option for D2D discovery signal design is discussed. For the fourth example option, the position of the discovery DM-RS follows a similar principle to DM-RS in DL subframes for transmission modes (TM)8and9physical DL shared channel (PDSCH) transmission. More specifically, for restricted D2D discovery, the discovery DM-RS can be generated according to 3GPP TS 36.211, Section 6.10.3. For open D2D discovery, the discovery DM-RS can be generated as follows. Note that in this case, ProSe enabled UE can randomly choose one antenna port for discovery signal transmission.

For any of the antenna ports pε{7, 8, . . . , 10}, the reference-signal sequence r (m) is defined by

The pseudo-random sequence c(i) is defined in 3GPP TS 36.211, Section 7.2. The pseudo-random sequence generator will be initialized at the start of each subframe with:

FIGS. 12 and 13illustrate the fourth example option for discovery signal design for the first subframe.FIG. 12illustrates discovery signal structures1200a,1200b, and1200cfor antenna ports 7 and 8.FIG. 13illustrates discovery signal structures1300a,1300b, and1300cfor antenna ports 9 and 10. Note that for second and subsequent subframes in 1×Nftime-frequency resource mapping, a guard period in the first OFDM symbol of the second and subsequent subframes is not needed; hence the mapping rule can follow the same principle as defined in 3GPP TS 36.21, Section 6.10.3. Similar to the third example option, the data symbol is constructed according to OFDMA technique, and the first OFDM symbol is punctured, in one embodiment, to ensure a proper guard period.

FIGS. 14 and 15illustrate discovery performance for blind detection. For open discovery, a ProSe enabled device may randomly select the DM-RS sequences when transmitting the discovery packet. As discussed above, from the reception UE perspective, discovering UEs need to perform blind detection of a DM-RS sequence to ensure the appropriate channel estimation and timing and frequency offset compensation. In particular, if a UL DM-RS is selected as discovery DM-RS, a DM-RS blind detection algorithm (implemented by the blind sequence detection component316) finds the candidate sequence with maximum correlation energy to determine the cyclic shift of the DM-RS sequence.

FIG. 14illustrates the discovery performance with DM-RS blind detection in the case without co-channel interference for a D2D discovery structure according to the second example option discussed above. From the plots, it can be seen that the performance degradation is negligible with DM-RS blind detection. This is primarily due to the fact that DM-RS miss detection probability is well below 10−3block error rate (BLER) in the operating signal-to-interference ratio (SINR) range for discovery, such as approximately 4 dB.

FIG. 15illustrates the discovery performance with DM-RS blind detection under co-channel interference for a D2D discovery structure according to the second example option discussed above. In the simulations, a fixed 30 dB SNR is assumed, and a DM-RS cyclic shift of the interference UE is distinct from that of target UE. Based on the simulation results, it is interesting to note that DM-RS blind detection can significantly improve the overall discovery performance by exploiting the inherent selection diversity, under the assumption that interference UE transmits the valid packet with distinct cyclic shift, and interference signal power is in a close range of target signal power.

FIG. 16is a schematic flow chart diagram illustrating a method1600for D2D discovery. In one embodiment, the method1600is performed by a mobile device, such as the UE102ofFIG. 3. In one embodiment, the UE102may perform the method1600prior to establishing a D2D session with one or more other UEs.

The method1600begins and a reference signal component308randomly selects1602a sequence for a reference signal. The reference signal component308may select1602the sequence by selecting an index for a cyclic shift or an orthogonal cover code for a predetermined base sequence. The reference signal component308may select1602the signal using a random number generator. In one embodiment, the reference signal component308selects1602the sequence for a reference signal for transmission in an open device-to-device discovery packet. The reference signal component308selects1602the sequence for a DM-RS or SRS.

A guard period component310determines1604a guard period for the discovery transmission. For example, the guard period component310may determine1604a first symbol signal for transmission during a partially punctured first symbol of the device-to-device discovery packet. In one embodiment, the guard period component310determines1604the guard period by generating a punctured first symbol. The guard period component310may generate a first symbol similar to the first symbols illustrated inFIGS. 5 and 6.

A transmission component312transmits1606a D2D discovery packet. In one embodiment, the transmission component312may transmit606a D2D discovery packet that includes a guard period determined1604by the guard period component310. In one embodiment, the transmission component312may transmit1606a D2D discovery packet that includes a reference signal generated based on the sequence selected1602by the reference signal component308. In one embodiment, the transmission component312transmits1606a D2D discovery packet that includes a punctured first symbol. The punctured first symbol may include a reference signal or may include data.

FIG. 17is a schematic flow chart diagram illustrating another method1700for D2D discovery. In one embodiment, the method1700is performed by a mobile device, such as the UE102ofFIG. 3. In one embodiment, the UE102may perform the method1700prior to establishing a D2D session with one or more other UEs.

The method1700begins and a receiver component304receives1702a message from a base station allocating licensed wireless resources for D2D discovery. In one embodiment, the receiver component304receives1702the message from an eNodeB110allocating one or more resource blocks for D2D discovery. In one embodiment, the allocated wireless resources include licensed resources for a cellular network.

A reference signal component308determines1704a random sequence for a reference signal for the licensed wireless resources. A transmission component312transmits1706D2D discovery information during the allocated licensed resources and also transmits1708a reference signal based on the random sequence. For example, the transmission component312may transmit a reference signal and discovery information according to any of the embodiments ofFIGS. 4-13. The method1700may also include establishing a D2D session with one or more proximal UEs.

FIG. 18is a schematic flow chart diagram illustrating another method1800for D2D discovery. In one embodiment, the method1800is performed by a mobile device, such as the UE102ofFIG. 3. In one embodiment, the UE102may perform the method1800prior to establishing a D2D session with one or more other UEs.

The method1800begins and a discovery information component314receives1802open P2P discovery information. The discovery information includes a reference signal transmitted by a source device using an unknown reference signal sequence. For example, the source device may have generated the reference signal based on a random cyclic shift index or orthogonal cover code index.

The blind sequence detection component316determines1804the unknown reference signal sequence. For example, the blind sequence detection component316may determine1804the unknown sequence by identifying a candidate sequence with a maximum correlation energy to the actual received reference signal. The channel component318estimates1806the channel between the source device and the UE102based on the reference signal. In one embodiment, the method1800includes transmitting a request to establish a D2D session with the source device.

FIG. 19is a schematic flow chart diagram illustrating yet another method1900for D2D discovery. In one embodiment, the method1900is performed by a mobile device, such as the UE102ofFIG. 3. In one embodiment, the UE102may perform the method1900prior to establishing a D2D session with one or more other UEs.

The method1900begins and a receiver component304receives1902, with a radio in a reception mode, a DL transmission from a radio access network. For example, the receiver component304may receive a DL transmission from an eNodeB110.

A communication mode component302switches1904the radio of the UE102from the reception mode to a transmission mode. In one embodiment, the communication mode component302switches1904the communication mode in preparation for a resource allocated for D2D discovery. A transmission component312transmits1906a D2D discovery packet during an OFDM resource block. The resource block may include a guard period in a first symbol of the OFDM resource block. In one embodiment, the guard period provides enough time for the radio to ramp up power and transmit the discovery packet.

FIG. 20is an example illustration of a mobile device, such as a user equipment (UE), a mobile station (MS), a mobile wireless device, a mobile communication device, a tablet, a handset, or another type of wireless communication device. The mobile device can include one or more antennas configured to communicate with a transmission station, such as a base station (BS), an eNB, a base band unit (BBU), a remote radio head (RRH), a remote radio equipment (RRE), a relay station (RS), a radio equipment (RE), or another type of wireless wide area network (WWAN) access point. The mobile device can be configured to communicate using at least one wireless communication standard, including 3GPP LTE, WiMAX, high speed packet access (HSPA), Bluetooth, and Wi-Fi. The mobile device can communicate using separate antennas for each wireless communication standard or shared antennas for multiple wireless communication standards. The mobile device can communicate in a wireless local area network (WLAN), a wireless personal area network (WPAN), and/or a WWAN.

FIG. 20also provides an illustration of a microphone and one or more speakers that can be used for audio input and output from the mobile device. The display screen may be a liquid crystal display (LCD) screen or other type of display screen, such as an organic light emitting diode (OLED) display. The display screen can be configured as a touch screen. The touch screen may use capacitive, resistive, or another type of touch screen technology. An application processor and a graphics processor can be coupled to internal memory to provide processing and display capabilities. A non-volatile memory port can also be used to provide data input/output options to a user. The non-volatile memory port may also be used to expand the memory capabilities of the mobile device. A keyboard may be integrated with the mobile device or wirelessly connected to the mobile device to provide additional user input. A virtual keyboard may also be provided using the touch screen. The screen and/or an input device, such as the keyboard or touch screen, may provide a user input interface for a user to interact with the mobile device.

EXAMPLES

The following examples pertain to further embodiments.

Example 1 is a wireless communication device configured to receive a message from a base station allocating licensed wireless resources for D2D discovery. The wireless communication device is configured to determine a random sequence for a reference signal for the licensed wireless resources. The reference signal comprises an LTE PUSCH DM-RS. The wireless communication device is configured to transmit D2D discovery information during the allocated licensed resources. The wireless communication device is configured to transmit a reference signal based on the random sequence.

In Example 2, the reference signal of Example 1 is transmitted during a fourth symbol and tenth symbol of each resource block of the allocated licensed wireless resource in the normal cyclic prefix case and during a third symbol and ninth symbol of each resource block in the extended cyclic prefix case.

In Example 3, determining the random sequence in any of Examples 1-2 optionally includes randomly selecting an orthogonal cover code for a base sequence.

In Example 4, determining the random sequence in any of Examples 1-3 optionally includes selecting the random sequence comprises selecting a cyclic shift for a base sequence.

In Example 5, transmitting the D2D discovery information of any of Examples 1-4 optionally includes transmitting an open discovery packet.

Example 6 is a UE that includes a radio configured to transmit and receive signals in a licensed wireless spectrum as well as a receiver component, a communication component, and a transmission component. The receiver component is configured to receive, with the radio in a reception mode, a downlink transmission from a radio access network. The communication mode component configured to switch the radio from the reception mode to a transmission mode. The transmission component is configured to transmit a D2D discovery packet during an OFDM resource block. Transmitting the D2D discovery packet includes transmitting a first symbol of the OFDM resource block having a guard period.

In Example 7, transmitting the first symbol including a guard period in Example 6 optionally transmitting the first symbol with an unused first portion of the first symbol and a used portion of the first symbol, wherein the first portion precedes the second portion in time.

In Example 8, the first portion of the first symbol of Example 7 optionally has a length of about 20 milliseconds or more.

In Example 9, the first portion of the first symbol of any of Examples 7-8 optionally includes about one-third of the first symbol.

In Example 10, the first portion of the first symbol of any of Examples 7-8 optionally includes comprises about one-half of the first symbol.

Example 11 is a device for open P2P discovery in a 3GPP LTE protocol that includes a discovery information component, a blind sequence detection component, and a channel component. The discovery information component is configured to receive open P2P discovery information. The discovery information includes a reference signal transmitted by a source wireless communication device using an unknown reference signal sequence. The blind sequence detection component is configured to determine the unknown reference signal sequence. The channel component is configured to estimate a channel between the device and the source wireless communication device based on the reference signal.

In Example 12, the device of Example 11 optionally further includes a scheduling component configured to receive a message from a 3GPP LTE network infrastructure allocating licensed wireless resources for P2P discovery. The discovery information component receives the open P2P discovery information during the allocated wireless resources.

In Example 13, the blind sequence detection component of any of Examples 11-12 is optionally configured to determine the unknown reference signal sequence by comparing the reference signal with one or more potential cyclic shifts for a base sequence.

In Example 14, the blind sequence detection component of any of Examples 11-13 is optionally configured to determine the unknown reference signal sequence by comparing the reference signal with one or more potential orthogonal cover codes for a base sequence.

In Example 15, the unknown reference signal sequence of any of Examples 11-14 includes a DM-RS.

In Example 16, the device of any of Examples 11-15 optionally includes one or more of, a processor, an antenna, a display, a speaker, and a user input interface.

Example 17 is a UE that includes a reference signal component, a guard period component, and a transmission component. The reference signal component is configured to randomly select a sequence for a reference signal for transmission in an open D2D discovery packet. The guard period component is configured to determine a first symbol signal for transmission during a first symbol of the D2D discovery packet, wherein the first symbol includes a partially punctured symbol. The transmission component is configured to transmit the D2D discovery packet. The D2D discovery packet includes the first symbol having the partially punctured symbol and a reference signal based on the randomly selected sequence.

In Example 18, the guard period component of Example 17 optionally determines the partially punctured symbol by determining a repeating signal during the first symbol.

In Example 19, the transmission component of any of Examples 17-18 optionally transmits the first symbol of the discovery packet without power on a fraction of the plurality of subcarriers based on a RPF, wherein the fraction comprises (RPF-1)/RPF. The RPF corresponds to a number of times that the repeating signal repeats.

In Example 20, the reference signal of any of Examples 17-19 is transmitted during a first symbol of each resource block of the D2D discovery packet.

Example 21 is a method for D2D discovery. The method includes receiving a message from a base station allocating licensed wireless resources for D2D discovery. The method includes determining a random sequence for a reference signal for the licensed wireless resources. The reference signal includes an LTE PUSCH DM-RS. The method includes transmitting D2D discovery information during the allocated licensed resources. The method includes transmitting a reference signal based on the random sequence.

In Example 22, the reference signal of Example 21 is transmitted during a fourth symbol and tenth symbol of each resource block of the allocated licensed wireless resource in the normal cyclic prefix case and during a third symbol and ninth symbol of each resource block in the extended cyclic prefix case.

In Example 23, determining the random sequence in any of Examples 21-22 optionally includes randomly selecting an orthogonal cover code for a base sequence.

In Example 24, determining the random sequence in any of Examples 21-23 optionally includes selecting the random sequence comprises selecting a cyclic shift for a base sequence.

In Example 25, transmitting the D2D discovery information of any of Examples 21-24 optionally includes transmitting an open discovery packet.

Example 26 is a method for D2D discovery. The method includes receiving, with a radio in a reception mode, a downlink transmission from a radio access network. The method includes switching the radio from the reception mode to a transmission mode. The method includes transmitting a D2D discovery packet during an OFDM resource block. Transmitting the D2D discovery packet includes transmitting a first symbol of the OFDM resource block having a guard period.

In Example 27, transmitting the first symbol including a guard period in Example 26 optionally transmitting the first symbol with an unused first portion of the first symbol and a used portion of the first symbol, wherein the first portion precedes the second portion in time.

In Example 28, the first portion of the first symbol of Example 27 optionally has a length of about 20 milliseconds or more.

In Example 29, the first portion of the first symbol of any of Examples 27-28 optionally includes about one-third of the first symbol.

In Example 30, the first portion of the first symbol of any of Examples 27-28 optionally includes comprises about one-half of the first symbol.

Example 31 is a method for open P2P discovery in a 3GPP LTE protocol. The method includes receiving open P2P discovery information. The discovery information includes a reference signal transmitted by a source wireless communication device using an unknown reference signal sequence. The method includes determining the unknown reference signal sequence. The method includes estimating a channel between the device and the source wireless communication device based on the reference signal.

In Example 32, the method of Example 31 optionally further includes receiving a message from a 3GPP LTE network infrastructure allocating licensed wireless resources for P2P discovery. The open P2P discovery information may be received during the allocated wireless resources.

In Example 33, determining the unknown reference signal sequence of any of Examples 31-32 optionally includes comparing the reference signal with one or more potential cyclic shifts for a base sequence.

In Example 34, determining the unknown reference signal sequence of any of Examples 31-33 optionally includes comparing the reference signal with one or more potential orthogonal cover codes for a base sequence.

In Example 35, the unknown reference signal sequence of any of Examples 31-34 includes a DM-RS.

Example 36 is a method for D2D discovery. The method includes randomly selecting a sequence for a reference signal for transmission in an open D2D discovery packet. The method includes determining a first symbol signal for transmission during a first symbol of the D2D discovery packet, wherein the first symbol includes a partially punctured symbol. The method includes transmitting the D2D discovery packet. The D2D discovery packet includes the first symbol having the partially punctured symbol and a reference signal based on the randomly selected sequence.

In Example 37, determining the first symbol of Example 16 optionally includes determining a repeating signal during the first symbol.

In Example 38, transmitting the first symbol of any of Examples 36-37 optionally includes transmitting the first symbol of the discovery packet without power on a fraction of the plurality of subcarriers based on a RPF, wherein the fraction comprises (RPF-1)/RPF. The RPF corresponds to a number of times that the repeating signal repeats.

In Example 39, the reference signal of any of Examples 36-38 is transmitted during a first symbol of each resource block of the D2D discovery packet.

Example 40 is an apparatus including means to perform a method in any of Examples 21-39.

Example 41 is a machine readable storage including machine-readable instructions, when executed, to implement a method or realize an apparatus of any of Examples 21-40.

It should be understood that many of the functional units described in this specification may be implemented as one or more components, which is a term used to more particularly emphasize their implementation independence. For example, a component may be implemented as a hardware circuit comprising custom very large scale integration (VLSI) circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A component may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices, or the like.

Components may also be implemented in software for execution by various types of processors. An identified component of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions, which may, for instance, be organized as an object, a procedure, or a function. Nevertheless, the executables of an identified component need not be physically located together, but may comprise disparate instructions stored in different locations that, when joined logically together, comprise the component and achieve the stated purpose for the component.