WO2006075277A1

WO2006075277A1 - Method and apparatus for multicast communication in wireless communication networks

Info

Publication number: WO2006075277A1
Application number: PCT/IB2006/050070
Authority: WO
Inventors: Dan Shang; Li Sun; Yonggang Du
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-01-12
Filing date: 2006-01-09
Publication date: 2006-07-20

Abstract

A multicast communication method to be executed by a network system, for supporting Peer-to-Peer (P2P) communication mode, comprising: receiving a multicast request from a sender UE, which contains ID information of multiple receiver UEs; determining whether P2P communication direct link between the sender UE and each of the receiver UEs meet requirements for establishing multicast communication, according to the multicast request; assigning corresponding radio resource to the sender UE and each of the receiver UEs if the requirements for establishing multicast communication are met, so that each of the receiver UEs can receive the traffic data from the sender UE.

Description

METHOD AND APPARATUS FOR MULTICAST COMMUNICATION IN WIRELESS COMMUNICATION NETWORKS

FIELD OF THE INVENTION

The present invention relates generally to a communication method and apparatus, and more particularly, to a method and apparatus for multicast communication in wireless communication networks.

BACKGROUND ART OF THE INVENTION

With the development of information technology, the conventional one-to-one unicast communication style could not meet customers' requirements. In many cases, the customer as sender hopes to send same data to multiple receivers, or namely performs multicast communication between a single sender and multiple receivers. The teleconference service, which burgeoned in recent years, is a typical application of the multicast communication. In the teleconference, when a speaker launches his speech, other attendants can hear the contents without presence at the meeting site through the communication channel established between the speaker and each of other attendants by a user terminal (for example, fixed-line or mobile phone). For the present, Ethernet, conventional telecommunication networks and conventional wireless communication network can all support multicast communication.

Since one User Equipment (UE) has to communicate with another UE through the relay of base station in conventional wireless communication systems, the multicast communication in conventional wireless communication system also requires the relay of base station as well. Fig. 1 shows the conventional UP-UTRAN-DOWN mode in

TD-SCDMA system, wherein UEl and UE2 exchange information through the UTRAN (Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network), which is composed of Base station Transceiver (Node B) and RNC (Radio Network Controller). Based on such UP-UTRAN-DOWN mode, when UEl ( called sender UE) attempts to send traffic data to multiple UEs (called receiver UEs, e.g. UE2 and UE3) at the same time, that is, performing multicast communication, UEl needs to send traffic data to UTRAN in the first instance, and then UTRAN forwards the traffic data to UE2 and UE3. When the multicast communication is performed under the conventional communication mode as illustrated in Fig. 1, the traffic data have to be relayed by base station no matter how far away between sender UE and each receiver UE. However, in some cases, for example, in the case of very short distance between each of the conference attendants, if the base station is still used to relay the traffic data for multicast communication, the radio resource will be surely wasted, and also, the transmission of traffic data will be inevitably delayed.

One method and apparatus for direct peer-to-peer (P2P) communication mode in case of close distance between two UEs in wireless communication networks are disclosed in the patent application titled "A Method and Apparatus for Establishing P2P

Communication in Wireless Communication Networks" and filed by KONINKLIJKE PHILIPS ELECTRONICS N. V. on March 7, 2003, with the Application Serial No. 03119892.9, which is incorporated herein as reference.

Fig. 2 illustrates the P2P communication mode. In Fig.2, the dashed line stands for signaling link while the solid line stands for data link, and the arrow shows the direction of information flow. As shown in Fig.2, only signaling link exists between the UTRAN and the UE, while only data link exists between the two communicating UEs. Assuming that the radio resource is required only for basic communication, if one direct link is used as one resource unit (RU) (with fixed carrier frequency, timeslot and spreading code), it is quite easy to deduce that P2P communication mode only needs 2 radio resource units to maintain the basic communication. If some extra overheads for signaling and supervision are ignored, P2P communication can save almost up to 50% radio resource compared with conventional communication mode; In the meantime, since there exists signaling links between UTRAN and UEs, UTRAN is still in control of P2P communication.

Obviously, when the distances between sender UE and each of receiver UEs for multicast communication are short, if the P2P communication mode can be introduced into multicast communication, it would be a more reasonable communication mode to save radio resource.

OBJECT AND SUMMARY OF THE INVENTION

One object of the present invention is to provide a multicast method in P2P- enabled communication systems, with which the radio resource will be significantly saved and traffic data's transmission delay will be effectively reduced, compared with conventional multicast communication modes.

In order to realize the object of the present invention, it's provided a multicast communication method to be executed by a network system, for supporting Peer-to-Peer

(P2P) communication mode, comprising: receiving a multicast request from a sender UE, which comprises ID information of multiple receiver UEs; determining whether P2P communication direct link between the sender UE and each of the receiver UEs meet requirements for establishing multicast communication, according to the multicast request; assigning corresponding radio resource to the sender UE and each of the receiver UEs if the requirements for establishing multicast communication are met, so that each of the receiver UEs can receive the traffic data from the sender UE.

In order to realize the object of the present invention, A multicast communication method to be executed by a UE for supporting P2P-enabled communication mode, comprising: sending a multicast request to a network system, which contains ID information of multiple receiver UEs; receiving radio resource for multicast communication assigned by the network system according to the multicast request; sending traffic data to each of the receiver UEs via direct links for the P2P communication by utilizing the radio resource. In order to realize the object of the present invention, it's provided a multicast communication method to be executed by a UE, for supporting Peer-to-Peer communication mode, comprising: receiving paging information from a network system according to multicast request from a sender UE; sending response information to the network system, which contains position information of the UE and/or P2P capability indication.

In order to realize the object of this invention, it's provided a network system for supporting Peer-to-Peer communication mode, comprising: a receiving unit, for receiving a multicast request from a sender UE, which comprises ID information of multiple receiver UEs; a determining unit, for determining whether or not direct links for the P2P communication between the sender UE and each of the receiver UEs can meet requirements for multicast communication; an assigning unit, for assigning corresponding radio resource to the sender UE and each of the receiver UEs when the requirements for establishing multicast communication are met, so that each of the receiver UEs can receive traffic data from the sender UE.

In order to realize the object of the present invention, it's provided a UE for supporting Peer-to-Peer communication mode, comprising: a sending unit, for sending multicast request to a network system, which comprises ID information of multiple receiver UEs; a receiving unit, for receiving radio resource for multicast communication assigned by the network system according to the multicast request; the sending unit, for sending traffic data to each of the receiver UEs via the direct links for the P2P communication by utilizing the radio resource.

Other objects and attainments together with a fully understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed descriptions will be given below to the present invention in conjunction with specific embodiments and accompanying drawings, in which:

Fig. l is a schematic diagram illustrating the conventional communication mode in TD-SCDMA system; Fig.2 is a schematic diagram illustrating the P2P communication mode in TD-

SCDMA system;

Fig.3 is a schematic diagram illustrating the multicast communication based on the direct multicast communication mode according to the present invention;

Fig.4A and 4B are flowcharts illustrating the direct multicast communication in TD-SCDMA system according to an embodiment of the present invention;

Throughout the drawing figures, like reference numerals will be understood to refer to like parts and components.

DETAILED DESCRIPTION OF THE INVENTION According to the multicast communication method as provided in the present invention, since the P2P-enabled UE normally has the multicast capability, if sender UE and multiple receiver UEs are close to each other, following P2P communication mode, traffic data can be conveyed via the direct link for P2P communication between sender UE and each of receiver UEs respectively, so as to save radio resource effectively.

Fig. 3 is a schematic diagram illustrating communication network for the multicast communication according to the present invention. In the multicast communication, as shown in Fig. 3, following P2P communication mode, each of UEs (UEl, UE2, UE3, and UE4) maintains signaling link with UTRAN respectively, so that

UTRAN is still in control of each UE. Moreover, the P2P communication direct links are established between the sender UE (UEl) and each of receiver UEs (UE2, UE3, UE4) respectively.

During the multicast communication process, UEl utilizes the same radio resource assigned by UTRAN, which means sending traffic data via each of direct links with the same time slot, same carrier frequency and same spreading code. In the same time slot, each of UE2, UE3 and UE4, as the receiver, receives the traffic data from UEl via the direct links with UEl by using the corresponding radio resource assigned by UTRAN.

Since UEl sends traffic data to UE2, UE3 and UE4 simultaneously via each of the direct links without the UTRAN' s relay, the multicast communication method in the present invention shown in Fig. 3 significantly saves radio resource. Besides, due to maintaining the signaling links with each of UEs (UEl, UE2, UE3, and UE4), UTRAN could realize the real-time control upon the undergoing multicast communication.

Now, the multicast communication method between a sender UE and multiple receiver UEs according to an embodiment of the present invention will be described in detail, by taking TD-SCDMA communication system as an example and in conjunction with Fig.4.

As shown in Fig. 4A and 4B, when UEl being in idle mode attempts to send traffic data to multiple UEs that are camping in a same cell by way of multicast communication, UEl sends a multicast request to network system UTRAN to initialize a random access procedure (Step SlO)

Wherein, UEl, acting as sender UE, can embed the ID information of each of receiver UEs (e.g. UE2, UE3 and UE4) with which UEl attempts to perform multicast communication into the multicast request. The ID information of the UEs, may be the receiver UEs' phone number, or other information that can identify each receiver UE. After receiving the multicast request, based on the ID information of each receiver UE, UTRAN sends paging messages to UE2, UE3 and UE4 respectively, and circulates the message that UEl attempts to act as sender UE to send traffic data to them by way of multicast communication (Step S20). Assuming that each receiver UE is in idle mode, after receiving the paging message, each of UE2, UE3 and UE4 sends a paging response message to UTRAN and enters connected mode respectively. (Step S30)

Wherein, the paging response message sent by each of receiver UEs (UE2, UE3, UE4) comprises the multicast capability indication for indicating whether the receiver UE is able to perform multicast communication (i.e. P2P capability indication).

Generally, a P2P-enabled UE owns the multicast capability.

Moreover, UTRAN can also acquire the position information of each receiver UE according to the paging response message. The position information could be the information that can be used to estimate the UE position, such as DOA of the paging response signal or the time when the paging response signal arrives at base station.

TRAN can also acquire the concrete position of UE by using Global Position System (GPS). The procedure of how UTRAN acquires UE's position can be implemented in various ways known in the prior art, and thus the detailed description is omitted here.

After receiving paging response messages from each receiver UE, UTRAN determines whether the predefined requirements for establishing multicast communication between UEl and each receiver UEs are satisfied according to the multicast capability indication and position information of each receiver UEs, which are contained in each paging response message (Step S40).

According to the multicast capability indication, UTRAN firstly determines whether or not each receiver UE is able to support multicast communication, that is: whether all of UE2, UE3 and UE4 can support multicast communication; next, according to each receiver UE's position information, UTRAN calculates the distance between each of receiver UE (UE2, UE3 and UE4) and UEl respectively so as to further determine if each receiver UE is camping within the P2P communication radio coverage of UEl. Based on the two answers of the above judgments, UTRAN determines whether or not to establish multicast communication between UEl and UE2, UE3, UE4.

(1) if all receiver UEs support multicast communication and also are camping within the P2P communication radio coverage of UEl, the predefined requirements of multicast communication are satisfied, that is, UTRAN confirms to establish multicast communication between UEl and UE2, UE3, UE4 (Step S50).

(2) If part of receiver UEs(e.g. UE2) do not support multicast communication, or part of receiver UEs (e.g. UE2) are not camping within the P2P communication radio coverage of UEl (Step S52), UTRAN reports the ID information of the part of the receiver UEs (e.g. UE2) to UEl (Step S54).

After receiving the ID information of the part of the receiver UEs that don't meet the requirements of multicast communication, based on real situation, UE will determine whether or not to continue the multicast communication with other receiver UEs that meet the requirements of multicast communication under the absence of this part of receiver UEs.

For example, in a teleconference, when a UE, acting as host, receives a report from network system that guest UE2 can't perform multicast communication, if the absence of UE2 may cause the discussion result of the teleconference invalid, UEl will ask to suspend this multicast communication; however, if UE2 is a unimportant attendant,

UEl may decide to continue the multicast communication.

UEl sends its decision to UTRAN as an indication (Step S58). If receiving the indication to suspend the multicast communication, UTRAN will terminate the operation of this multicast communication (Step SlOOO); whereas receiving the indication to continue the multicast communication, UTRAN will confirm to establish the multicast communication between UEl and the receiver UEs that satisfy the requirements of multicast communication

(3) If all receiver UEs don't support multicast communication, or all receiver UEs are outside the P2P communication radio coverage of UEl, UTRAN will terminate the operation of this multicast communication (Step SlOOO).

If the multicast communication are confirmed to be established, including the above scenario (1) and (2), UTRAN sends ID information of UEl that is acting as sender to each of above receiver UEs that are able to perform multicast communication, such as UE2, UE3, and UE4 in scenario (1), or UE3 and UE4 in scenario (2) (Step S60).

After receiving the UEl 's ID information sent from UTRAN, each receiver UE (e.g. UE2, UE3 and UE4) determines whether or not to permit to establish the multicast communication with UEl respectively (Step S70), and also feedbacks the result to UTRAN as an answer (Step S80).

According to the answer received from each receiver UE, UTRAN acquires the information whether or not each receiver UE permits to establish multicast communication with UEl (Step S85).

(i) If all of receiver UEs permit to establish multicast communication with UEl, UTRAN will confirm to establish the multicast communication between UEl and UE2, UE3, UE4(Step S90).

(ii) If part of receiver UEs (for example UE2) don't permit to perform multicast communication with UEl (Step S92), UTRAN will report the ID information of this part of receiver UEs(e.g. UE2) to UEl (Step S94).

After receiving ID information of the part of receiver UEs, according to real situation, UEl determines whether or not to continue the multicast communication with other receiver UEs that permit the multicast communication with it (e.g., UE3, and UE4) under the absence of this part of receiver UEs (Step S96), and also sends the decision result to UTRAN as an indication message (Step S98).

If receiving the indication to suspend multicast communication, UTRAN will terminate this multicast communication (Step SlOOO). If receiving the indication to continue the multicast communication, UTRAN will confirm to perform the multicast communication between UEl and other receiver UEs (e.g. UE3 and UE4) that permit multicast communication with UEl.

(iii) If all receiver UEs don't permit multicast communication with UEl, UTRAN will terminate this multicast communication (Step SlOOO)

The above ID information of UEl can also be combined with paging message at Step S30 and sent to each receiver UE by UTRAN, so that UTRAN can get the response message from each receiver UEs indicating whether or not they permit multicast communication with UEl.

If the multicast communication can be confirmed to establish at S90 and S96, including above two scenarios (i) and (ii), UTRAN will assign radio resource for probing the P2P direct links between UEl and each of receiver UEs to UEl and each of receiver UEs (e.g, UE2, UE3 and UE4 in scenario (i); UE3 and UE4 in scenario (ii)) (Step SlOO). The assigned radio resource includes carrier frequency, receiving/sending time slot and spreading code.

After receiver the radio resource assigned by UTRAN, UEl and each receiver UE

(e.g. UE2, UE3 and UE4) enter link probing mode. (Step SIlO). Utilizing the assigned radio resource, UEl sends probing signal to each receiver UE via each direct link respectively. (Step S 120)

Each receiving UE searches the probing signal on assigned radio channel (Step S 130), and determines if it can receive the probing signal from UEl within a predefined period of time (Step S140)

If receiving the probing signal within the predefined time period, the receiver UE sends a probing report to UTRAN, which includes the detected performance of the direct link between the receiver UE and UEl (Step S 142); if not receiving the probing signal within the predefined time period, the receiver UE will also send a probing report to UTRAN to indicate it can not receive the probing signal(Step S 144).

UTRAN receives the probing reports from each of receiver UEs (Step S 150), and checks if the direct link performance detected by each receiver UE that receives the probing signal can meet the requirements of communication quality(Step S 160).

(a) If the probing report from each receiver UE(e.g., UE2, UE3 and UE4) reveals that the probing of each direct link is successful, that is, the performance of each direct link can satisfy the communication quality requirements, for example, the detected link performance value is above a predefined threshold, so each of direct links can be used for multicast communication, UTRAN will assign radio resource for multicast communication to UEl and each receiver UE, so that UEl can send traffic data to each receiver UE via each direct link(Step S 170). (b). If the probing report from each receiver UE(e.g., UE2, UE3 and UE4) reveals that part of the direct links' performance doesn't meet the requirements of communication quality (for example, the direct link between UEl and UE2 can not satisfy the communication requirements) or part of the receiver UEs (e.g. UE2) have not received the probing signal within predetermined time period, so part of the direct links can't be used for multicast communication (Step S162) , that is, the probing for some of the direct links fails, UTRAN will report the ID information of the corresponding part of the receiver UEs(e.g., UE2) to UEl (Step S164). Receiving the ID information of the part of the receiver UEs, based on the real situation, UEl determines whether to continue multicast communication via other successfully probed direct link(Step S 166) with absence of this part of the receiver

UEs(Step S166), and sends the decision to UTRAN as an indication as well (Step S168).

When receiving the indication to suspend multicast communication, UTRAN will terminate the multicast communication (Step SlOOO); whereas receiving the indication to continue the multicast communication, UTRAN will confirm to perform the multicast communication via the successfully probed direct links.(e.g. the direct link between UEl and UE3, UEl and UE4) (Step S 170)

(c) If the probing report from each receiver UE(e.g., UE2, UE3 and UE4) reveals that the performance of all direct links doesn't meet the requirements of communication quality, and each direct link can not be used for multicast communication, that is, the probing for each direct link fails, UTRAN will then terminate the multicast communication (Step SlOOO).

At step S 170, the network assigns the radio resource for multicast communication to the successfully probed direct links. The assigned radio resource includes: carrier frequency, receiving/sending time slot, spreading code. On receiving assigned radio resource, UEl and each receiver UE (e.g., UE2, UE3 and UE4) enter multicast communication mode (Step S 180). Within the assigned sending time slot, UEl will send the traffic data modulated by the same spreading code with the same carrier frequency to each receiver UE via each of direct links (Step S 190). When the multicast communication ends, UEl sends UTRAN (via signaling link) and each receiver UE in multicast communication mode (via each direct link) an end multicast message, and releases corresponding radio resource (Step S200)

After receiving the end multicast message, each receiver UE release its occupied radio resource respectively (Step S210); UTRAN reclaims the radio resource for the multicast communication (Step S220).

The multicast method provided by the this invention is described in detail with above embodiment in conjunction with Fig. 4A and 4B , but the present invention is not limited to present embodiment, for example, the present invention not only applies to the multicast communication between a sender UE and multiple receiver UEs camped in a same cell, but also applies to the scenarios where sender UE and multiple receiver UEs are camping in different cells or are outside the cell's radio coverage.

When sender UE and multiple receiver UEs are camping in different cells, the procedures are same as that shown in the embodiment, except that the control information needs to be conveyed by two base stations. The conveying procedure of control information between two base stations can be referred to the patent applications titled "Method and Apparatus for Establishing P2P Communication Between UEs in Different Cells" and filed by KONINKLIJKE PHILIPS ELECTRONICS N.V. on Nov 27, 2003, with Application Serial No. 200310118646.1, which is incorporated herein as reference.

When sender UE and multiple UEs are outside the coverage of cell, the conveying procedure of control information can be referred to the patent applications titled "Billing Method and Apparatus for Offline P2P Communication" and filed by KONINKLIJKE PHILIPS ELECTRONICS N.V. on Aug 10, 2004, Application Serial No.

200410056540.8, which is incorporated herein as reference. Other procedures of multicast communication are same as that in the embodiment.

As to the above multicast method for use in P2P-enabled wireless communication networks as provided in the present invention, it can be implemented in software or hardware, or in combination of both.

Advantages of the Invention As described above, according to the multicast method and apparatus for use in P2P-enabled wireless communication networks in the present invention, when sender UE and multiple receiver UEs are close to each other, following P2P communication mode, traffic data can be conveyed via P2P communication direct links between sender UE and each of receiver UEs. Compared with the multicast communication based on conventional communication mode, this method can effectively save radio resource and reduce the traffic data transmission delay.

In the meantime, the control links still exist between each UE and UTRAN during the multicast communication, therefore multicast communication can be performed under the control and support of UTRAN, and can enable UTRAN to maintain the control of radio resource.

Moreover, the above multicast communication method, is provided in the present invention by taking TD-SCDMA as an example, but the method can also be applicable to TDD SCDMA system.

It is to be understood by those skilled in the art that multicast method and apparatus in P2P-enabled wireless communication networks as disclosed in this invention can be made of various modifications without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMS:

1. A multicast communication method to be executed by a network system, for supporting Peer-to-Peer (P2P) communication mode, comprising, (a) receiving a multicast request from a sender UE, which comprises ID information of multiple receiver UEs;

(b) determining whether P2P communication direct link between the sender UE and each of the receiver UEs meet requirements for establishing multicast communication, according to the multicast request; (c) assigning corresponding radio resource to the sender UE and each of the receiver UEs if the requirements for establishing multicast communication are met, so that each of the receiver UEs is able to receive the traffic data from the sender UE.

2. The multicast communication method according to claim 1, wherein the step (b) comprises:

(bl) sending paging information to each of the receiver UEs according to the multicast request;

(b2) receiving response information with respect to the paging information from each of the receiver UEs; (b3) determining if the requirements for establishing multicast communication are satisfied between the sender UE and each of the receiver UEs, according to the response information.

3. The multicast communication method according to claim 2, wherein the response information comprises P2P capability indication.

4. The multicast communication method according to claim 3, wherein the response information further includes the position information of the receiver UEs, and step (b3) further comprises: determining whether each of the receiver UEs able to perform multicast communication, according to the P2P capability indication; determining whether each of the receiver UEs is within P2P communication radio coverage of the sender UE, according to the position information; confirming that the multicast communication is able to be established between the sender UE and each of the receiver UEs, if all the receiver UEs support multicast communication and each of the receiver UEs is camping within the P2P communication radio coverage of the sender UE,

5. The multicast communication method according to claim 4, wherein step (b3) further comprises: reporting information of part of the receiver UEs to the sender UE, if the part of the receiver UEs don't support multicast communication, or the part of the receiver UEs are not camping within the P2P communication radio coverage of the sender UE; receiving an indication sent by the sender UE according to the report; determining whether multicast communication is able to be established between the sender UE and the receiver UEs, according to the indication.

6. The multicast communication method according to claim 1, further comprising:

(i) sending ID information of the sender UE to each of the receiver UEs respectively, according to the multicast request;

(ii) receiving answer information from each of the receiver UEs; (iii) determining whether each of the receiver UEs permits to perform multicast communication with the sender UE according to the answer information, so as to determine whether or not to establish multicast communication between the sender UE and each of the receiver UEs.

7. The multicast communication method according to claim 6, wherein, according to the multicast request, the sender UE sends paging information to each of the receiver

UEs respectively, wherein the paging information comprises the ID information of the sender UE.

8. The multicast communication method according to claim 6, wherein step (iii) comprises: reporting information of the part of the receiver UEs to the sender UE, if the part of the receiver UEs doesn't permit to perform multicast communication with the sender UE; receiving an indication sent by the sender UE according to the report; determining whether or not to establish multicast communication between the sender UE and each of the receiver UEs according to the indication.

9. The multicast communication method according to claim 1, wherein step (b) comprises:

(Bl) assigning radio resource for probing the direct link to the sender UE and each of the receiver UEs, so that the sender UE sends probing signal to each of the receiver UEs via the direct link; (B2) receiving probing reports from each of the receiver UEs;

(B3) determining whether multicast communication is performed via the direct link according to the probing reports, thereby determining whether the requirements for multicast communication are satisfied.

10. The multicast communication method according to claim 9, wherein step (B3) comprises: reporting information of the part of the receiver UEs to the sender UE, if the probing report reveals that the part of the receiver UEs is not able to receive the probing signal within a predefined period of time, or performance of the direct links between the part of the receiver UEs and the sender UE is not meet the quality requirements for multicast communication; receiving an indication sent by the sender UE according to the report; determining whether or not to perform multicast communication via the direct link according to the indication.

11. A multicast communication method to be executed by a UE for supporting P2P- enabled communication mode, comprising:

(a) sending a multicast request to a network system, which comprises ID information of multiple receiver UEs; (b) receiving radio resource for multicast communication assigned by the network system according to the multicast request;

(c) sending traffic data to each of the receiver UEs via direct links for the P2P communication by utilizing the radio resource.

12. The multicast communication method according to claim 11, wherein step (b) comprises: receiving radio resource assigned by the network system for probing the direct links; sending probing signal to each of the receiver UEs by utilizing the radio resource.

13. The multicast communication method according to claim 12, further comprising: (i) receiving a report from the network system, wherein the report indicates that part of the receiver UEs don't support multicast communication;

(ii) determining whether or not to establish multicast communication with the receiver UEs according to the report;

(iii) sending the determination result to the network system as an indication.

14. The multicast communication method according to claim 13, wherein step (i) comprises: receiving a report from the network system, wherein the report indicates that the part of the receiver UEs don't permit to establish multicast communication with the UE.

15. The multicast communication method according to claim 14, wherein step (i) further comprises: receiving a report from the network system, wherein the report indicates that part of the receiver UEs is not able to receive the probing signal within a predefined period of time, or performance of the direct links between the part of the receiver UEs and the sender UE is not meet the quality requirements for multicast communication.

16. A multicast communication method to be executed by a UE, for supporting Peer-to-Peer (P2P) communication mode, comprising: receiving paging information from a network system according to multicast request from a sender UE; sending response information to the network system, which comprises position information of the UE and/or P2P capability indication.

17. A network system for supporting Peer-to-Peer (P2P) communication mode, comprising: a receiving unit, for receiving a multicast request from a sender UE, which comprises ID information of multiple receiver UEs; a determining unit, for determining whether or not direct links for the P2P communication between the sender UE and each of the receiver UEs meet requirements for multicast communication; an assigning unit, for assigning corresponding radio resource to the sender UE and each of the receiver UEs when the requirements for establishing multicast communication are met, so that each of the receiver UEs is able to receive traffic data from the sender UE.

18. The network system according to claim 17, further comprising: a sending unit, for sending paging information to each of the receiver UEs respectively according to the multicast request; the receiving unit, for receiving response information with respect to the paging information from each of the receiver UEs, wherein the response information comprises

P2P capability indication; the determining unit, for determining whether or not the requirements for establishing multicast communication are met between the sender UE and each of the receiver UEs.

19. The network system according to claim 17, wherein the response information further comprises position information of the receiver UEs, and the determining unit, for determining whether or not each of the receiver UEs is able to perform multicast communication according to the P2P capability indication, and also, determining whether or not each of the receiver UEs is camping within the P2P communication radio coverage of the sender UE; and confirming to establishing multicast communication between the sender UE and each of the receiver UEs, if each of the receiver UEs supports multicast communication, and is camping within the P2P communication radio coverage of the sender UE.

20. The network system according to claim 19, wherein: the assigning unit, for assigning radio resource for probing the direct links to the sender UE and each of the receiver UEs, so that the sender UE sends probing signal to each of the receiver UEs via the direct links; the receiving unit, for receiving probing reports from each of the receiver UEs; the determining unit, for determining whether the multicast communication via the direct links is able to be performed according to the probing report, thereby determining whether or not the requirements for establishing multicast communication are met.

21. A UE for supporting Peer-to-Peer communication mode, comprising: a sending unit, for sending multicast request to a network system, which comprises ID information of multiple receiver UEs; a receiving unit, for receiving radio resource for multicast communication assigned by the network system according to the multicast request; the sending unit, for sending traffic data to each of the receiver UEs via the direct links for the P2P communication by utilizing the radio resource.

22. The UE according to claim 21, wherein: the receiving unit, for receiving radio resource assigned by the network system for probing direct link; the sending unit, for sending probing signal to each of the receiver UEs by utilizing the radio resource.

23. The UE according to claim 21 or 22, wherein: the receiving unit, for receiving paging information from a network system according to a multicast request from a sender UE; the sending unit, for sending response information, which comprises the UE's position information and / or P2P capability indication, to the network system.