畢設(shè)匯總3蔡沅沅翻譯原文

1、Device-to-Device Communication as an Underlay to LTE-Advanced NetworksKlaus Doppler, Mika Rinne, Carl Wijting, Cssio B. Ribeiro, and Klaus Hugl, Nokia Research CenterABSTRACTIn this article device-to-device (D2D) com- munication underlaying a 3GPP LTE-Advanced cellular network is studied as an enabl

2、er of local services with limited interference impact on the primary cellular network. The approach of the study is a tight integration of D2D communica- tion into an LTE-Advanced network. In particu-has benefits, as it can guarantee a planned (inter- ference) environment tead of an uncoordinat- ed

3、one. Hence, it could be more convenient for local service providers to make investment deci- sions based on access to the licensed spectrum compared to the unlicensed spectrum. However, the access should be granted with small enough expenses, not comparable to the license fees of cellular operators.

4、A cellular operator may offer such a cost effi- cient access to the licensed spectrum enabled by D2D communication as a controlled or con- strained underlay to an IMT-Advanced cellular network, as we earlier proposed in 2. In this article we present the necessary additions to an LTE-Advanced network

5、 to enable D2D session setup and management. We outline a solution for a D2D session setup using dedicated signal- ing and automatic handover of network routed traffic to D2D links between nearby (proximity) devices. Furthermore, we present the interfer- ence coordination mechanisms that enable unde

6、rlay D2D communication and present results on the achievable D2D throughput in a worst case interference limited local area sce- nario.The concept of D2D communication as anunderlay to a cellular network, operating on the same resources, is illustrated in Fig. 1. Besides cellular operation, where us

7、er equipment (UE) is served by the network via the base stations, called evolved NodeBs (eNBs) in the LTE archi- tecture, UE units may communicate directly with each other over the D2D links. The UE in D2D connections rema controlled by the eNBs and continue cellular operation.The eNBs can control t

8、he resources used for cellular communications and by the D2D link. The eNBs can also set constraints on the trans- mit power of D2D transmitters to limit the inter- ference experienced at the cellular receivers. Resources can also be assigned to D2D links in the case of a dense LTE network with high

9、 net- work load, where a cognitive radio with a cellu- lar network as the primary service would not be able to detect locally unused spectrum (i.e., “white spaces”).In addition, 3GPP has introduced a femto base station solution. For femto, small isolated cells can be set up by the consumers themselv

10、es, when allowed by the operator, to increase spatial reuse of the operators spectrum. Femtocellslar, we proposemechanismsfor D2Dcommunication session setup and managementinvolving procedures in the LTE System Archi- tecture Evolution. Moreover, we present numer- ical results based on system simulat

11、ions in an interference limited local area scenario. Our results show that D2D communication can increase the total throughput observed in the cell area.INTRODUCTIONMajor effort has been put in recent years on the development of Third Generation Partnership Project (3GPP) Long Term Evolution (LTE),

12、which provides Evolved Universal Mobile Telecommunications System (UMTS) terrestrial radio access (EUTRA) and EUTRA network (EUTRAN) technology for higher data rates and system capacity, and the System Architec- ture Evolution (SAE) for efficient networking and cost saving operation.3GPP has recentl

13、y defined a further study item for LTE-Advanced, which shall prepare new technology components for LTE to meet the IMT- Advanced requirements, also in the local areascenario.IMT-Advancedwillofferhighbandwidths up to 100 MHz for higher data rates, global operation, and economy of scale to supporta wi

14、de range of services. Such future radio access systems will be scalable in terms of carrier bandwidth and carrier frequencies on various spectrum bands 1. This article intro- duces a technology component for LTE- Advanced that has so far not been considered sufficiently: device-to-device (D2D) commu

15、nica- tion as an underlay to cellular networks.In recent years wireless local area networks(WLANs) have become increasingly popular, as they enable access to the Internet and local ser- vices with low-cost infrastructure, and cheap and fast access to the spectrum in the license exempt bands. However

16、, operation on a licensed band420163-6804/09/$25.00 2009 IEEEIEEE Communications Magazine December 2009TOPICS IN RADIO COMMUNICATIONSrequire access to the cellular core network (by fixed Internet connectivity), and the radioApplications and services based on D2D communications can be manifold. As a

17、motivat- ing example, consider a use case where a local media server is set up at a rock concert to offer a huge amount of promotional material for visi- tors to download. At the same time, there is a need to handle phone calls reliably and provide Internet access without congestion that would be ca

18、used by the additional load due to the media server. While the cellular network is serving phone calls and Internet connectivity, D2D com- munications can provide an efficient solution for the local media service. D2D communication can be utilized to download promotional materi- al to UE as well as

19、to distribute it among UE. BitTorrent can be used for this, as an example.D2D operation can be fairly transparent tothe user, who simply enters a request for a uni- form resource locator (URL) at the UE. The network is able to detect that the request is sent to the local media server, and it therefo

20、re hands the communication over to a D2D connection. Existing technologies such as Bluetooth or WLAN do not provide a satisfactory solution. For example, Bluetooth requires manual device pairing, and WLAN may require user-defined settings for the access points. Additionally, unli- censed spectrum op

21、eration of Bluetooth and WLAN causes uncertainty as to whether the spectrum and services are truly available. This results in a trial-and-error process users do not appreciate.This article is organized as follows. We illus-trate how D2D communication can be estab- lished in an LTE-Advanced network h

22、aving an SAE architecture. The main contribution of the article is to draft the functionality and messagingFigure 1. Device-to-device communication between UE1 and UE2 as an underlay to a cellular network. The red shaded area indicates potential inter- ference from D2D communication.Radio Service (G

23、PRS) to the SAE server archi- tecture. Session setup happens in the user plane using the Session Initiation Protocol (SIP). SAE provides connectivity to the Internet, where a SIP application server (AS) is found by a discovery procedure or operator assignment. The SAE architecture includes the mobil

24、ity management entity (MME) and the packet data network (PDN) gateway, which together take care of the UE context, setting up the SAE bearers, IP tun- nels, and IP connectivity between the UE and the serving PDN gateway. Figure 2 shows session setup by SIP (SIP invite) in the SAE architecture. After

25、 successful session setup, any two or more devices (UE, or UE and servers) may com- municate over the Internet. However, in peer-to- peer communication between devices in close proximity, the operator network need not be involved in the actual data transport except for signaling of the session setup

26、, charging, and poli- cy enforcement. Therefore, we propose to intro- duce a D2D communication mode to LTE- Advanced, and describe two options for session setup and management. In order to enable the D2D communication as an underlay operation to the LTE network, interference coordination is a prereq

27、uisite for D2D session setup to take place.Interference coordination is studied with afeasibility analysis.D2D SESSION SETUP BYDETECTING D2D TRAFFICIn the SAE architecture, the node in the net- work that is aware of wide-area (global) IP addresses is the gateway (serving PDN gateway).required to set

28、 up a D2D connectionide theSAE architecture, and also if the session setup takes place as an application layer signaling tothe Internet beyond the cellular network. We outline how the interference of D2D connec- tions to the cellular network can be limited. Both the uplink and downlink period of tim

29、e- division duplex operation of the cellular network is addressed because of their different natures in multiple access interference and power control.Finally, we present performance assessment results showing that D2D can operate efficiently with minor and controlled degradation of cellu- lar opera

30、tion. Here, we have chosen the chal- lenges of full load and an interference limited local area scenario. It is evident that the benefits from D2D operation during times of underuti- lized cellular resources and low load are even more prominent.LTE systems with the SAE architecture 3 oper- ate fully

31、 in the packet-switched domain using Internet protocols. SAE replaces a conventional circuit-switched connection to the mobile switch- ing center (MSC) and extends the General PacketIEEE Communications Magazine December 200943UE1UE2eNB1)A session is initiated by one of the UE units. 2)The gateway de

32、tects IP traffic originating from and destined to UE in the same sub-net and to be tunneled within the same serving eNB or between eNBs serving neighboring cells.3) If the traffic fulfills certain criteria (e.g., data rate), the gateway earmarks the traffic as potential D2D traffic.4) The eNB(s) req

33、uest measurements from the UE to check if D2D communication offers higher throughput.5) If both UE units are D2D capable and D2D communication offers higher throughput, the eNB(s) may set up a D2D bearer.6) Even if the D2D connection setup is suc- cessful, the eNB(s) still maintain the SAE bearer be

34、tween the UE and the gateway for cellular communications. Furthermore, theFigure 2. SIP session initiation in LTE-Advanced with SAE architecture.eNB maintathe radio resource controlfor both cellular and D2D communication.7) The UE will send/receive packets to/from the IP address of the peer UE using

35、 the D2D connection without the eNB or SAE being involved in routing.After the D2D bearer has been established between the peer devices, it is still necessary for the eNB to control the radio resources also used by the D2D communication. The UE may of course continue communication to the Internet, b

36、ecause the SAE bearer is maintained and theThe gateway keeps a routing table that enables IP routing from/to the Internet. The gateway is able to route IP packets to the proper eNBs serving the active destination UE. Similarly, the gateway receives IP packets from the source UE via the serving eNB a

37、nd routes them to the Internet. The IP transport from/to the eNBs happens in IP tunnels set-up by the MME in the Initial Attach of the UE to the gateway.The gateway is able to detect potential D2D traffic since it actually processes the IP headers of the data packets and tunnel headers, so it knows

38、by which eNB the UE is served. Potential D2D traffic is any flow whose tunnel endpoint identifiers match for both UE units (i.e., the source and destination IP addresses of the for- ward tunnel, and the destination and source addresses of the reverse tunnel are assigned to the same eNB), or when the

39、 tunnel endpoints are assigned to neighboring eNBs. The gateway may earmark packets of a potential D2D traffic flow as depicted in Fig. 3.As a next step, the eNB requests the UE to make measurements to check if the D2D devices are in communication range and if D2D commu- nication actually offers hig

40、her throughput than cellular communication (discussed in more detail later). If the transport conditions for D2D com- munication are favorable, the eNB sets up a D2D radio bearer directly between the two UE units so that they communicate over D2D com- munication resources. Thus, those IP packets wit

41、h an IP source address and an IP destination address of the peer UE having an active D2D connection need not be transmitted to the eNB and SAE gateway at all.D2D communication could also be estab- lished for UE served by different eNBs since the gateway is aware of the potential cell neighbor- hood.

42、 This is beneficial to avoid an excessive amount of traffic routed in the network, which could actually be classified as D2D traffic tead. In cases where the UE is in neighboring cells, the eNBs serving the UE have to coordi- nate D2D measurements and the D2D bearer setup over the X2 interface 3.The

43、 session setup requires the following steps:connectivity to the gateway rema. For thisactivity, the UE stays in the LTE_Active state and RRC_Connected state, respectively.In addition to checking if D2D offers bene- fits, the decision to establish a D2D connection can be based on a defined policy suc

44、h as limiting the number of D2D connections to keep the interference to the cellular network below a tol- erable level.A handover from a D2D connection to a cel- lular connection is initiated when the cellular connection achieves higher throughput than the D2D or if one of the policies for D2D conne

45、c- tions is violated.One important property of setting up a D2D connection by a trigger of detecting IP traffic between nearby devices is that it works for any peer-to-peer IP traffic without service differenti- ation. Thus, it is blind to the actual service. Sec- ond, it is transparent to the user

46、(i.e., the user does not have to select a special option for the D2D session). The D2D UE units are passive participants in the session setup, which is mainly handled at the MME and higher layers. Howev- er, the automatic switching between cellular and D2D connection should be reliable and seamless

47、to guarantee user satisfaction.D2D SESSION SETUP USING DEDICATED SAE SIGNALINGA session setup using dedicated SAE signaling avoids the overhead from detecting D2D traffic on the fly from IP packets. For this alternative, we propose to provide a specific address format to separate a D2D SIP session r

48、equest from a generic SIP session request. Furthermore, we propose to enhance the MME with a light SIP handler to facilitate session setup.44IEEE Communications Magazine December 2009U-planeUEeNBMMEPDN GWSIP ASUESIP invite SIPRRCSAE bearerSIP inviteSIPFigure 3. The gateway earmarks local traffic to

49、indicate potential D2D traffic to the eNB. The eNB can then check if the devices corresponding to these packets can set up a D2D connection.The new address format of D2D SIP could simply be usernamerealm.D2D_keyword, where the former part (usernamerealm) is a well-known SIP uniform resource indicato

50、r (URI), and the latter part (D2D_keyword) is a novel extension to let the SAE handle the local D2D session in a special way. The local exten- sion is easily distinguishable as a D2D address by a special D2D_keyword such as .direct, .local,.peer, or .short.In this approach, the application (or the u

51、ser) at the requesting UE needs to decide whether to prefer initiation of a D2D session or a regular session. We foresee the following options to aid this decision: The user explicitly selects a D2D session by selecting the SIP URI format with a local extension. The UE software detects the local ext

52、ension and encapsulates the SIP invite message into a control plane message to the MME tead of delivering it to a user planeTCP/IP or UDP/IP port.The D2D session setup is illustrated in Fig. 4, which presents the peer entities UE1 and UE2 with the application layer and IP layer protocols for session

53、 initiation and connectivity. Further- more, the radio resource control (RRC) proto- col is shown.In this case UE1 calls UE2 by SIP invite mes- sage using the .D2D_keyword extension with the URI of UE2. This lets the SAE network detect the preference for a local session, which leads to the setup of

54、a D2D bearer tead of (or in addi- tion to) SAE bearers. This setup procedure is local to the radio access network and does not involve a SIP server far away in the Internet, which leads to faster session setup.We propose to encapsulate the SIP invite message in an NAS control plane message. In the S

55、AE architecture, the MME receives all NAS messages from the served UE. The MME is in charge of the control plane functions like mobility management, and when needed it also communicates to the home subscriber server (HSS) to get subscriber records and take care of user authentication. We propose to

56、enhance the MME functionality by a light SIP handler to keep track of the SIP addresses of the UE ide the tracking area. This can be done at the initial access, when the UE registers to the network and the MME assigns the temporary mobile subscriber identity (TMSI) to the UE that is used for all con

57、trol of the UE in the wide area network. In the registration phase the HSS needs to be involved, but afterward the MME can handle the UE (mobility) con- text by itself.When receiving an NAS message type for aD2D session, the MME simply passes the SIP message contents to the light SIP handler, wherea

58、s other NAS messages are treated as usual. The NAS message delivery is defined in the SAE specifications, and the proposal in this article requires no changes to the transport of NAS messages as such.After handling the SIP message and detecting that the D2D UEs are in the same or neighbor- ing cells, the MME will request a setup of a D2D radio bearer from the serving eNB (or serving eNBs for D2D communi