Session 4. LTE in ns-3. 김선도 Multimedia & Wireless Networking Laboratory, SNU

Transcription

1 Session 4. LTE in ns-3 김선도 Multimedia & Wireless Networking Laboratory, SNU 1

2 LTE Overview LTE in ns-3 Simulation Examples Contents Packet Transmission Example In class Assignment 2

3 LTE Overview 3

4 3GPP LTE and LTE-A LTE (Long Term Evolution) LTE is 3GPP system for the years 2010 to 2020 and beyond It must keep the support for high mobility users like in GSM/UMTS Bandwidth: 1.4 MHz ~ 20 MHz Peak Data Rate: 300 Mbps (4x4 MIMO, 20 MHz) Key feature: AMC (Adaptive Modulation Coding), MIMO (up to 4x4) LTE-A (LTE Advanced) LTE-A is often used for LTE release 10 and beyond Bandwidth: up to 100 MHz Peak Data Rate: 3 Gbps Key feature: CA (Carrier Aggregation), MIMO (up to 8x8), CoMP (Coordinated Multi Point Transmission), HetNet (Heterogeneous Network), Relay 4

5 LTE System Architecture EPS Serving GW P-GW MME HSS enodeb: evolved Node B MME: Mobility Management Entity P-GW: Packet Data Network Gateway HSS: Home Subscriber Server 5

6 Key Entity enb (evolved Node B) It is the hardware that is connected to the mobile phone network Functions for radio resource management Scheduling and transmission MME (Mobility Management Entity) Tracking area list management Bearer management functions including dedicated bearer establishment S-GW (Serving Gateway) Packet routing and forwarding Mobility anchoring for inter-3gpp mobility P-GW (Packet Data Network Gateway) Per-user based packet filtering UE IP address allocation Mobility anchoring for non-3gpp mobility 6

7 Protocol Architecture 7

8 QoS and EPS Bearer EPS Bearers In order to support multiple QoS requirements, different bearers are setup within EPS Default EPS Bearer Establish when UE connects to PDN Provide always-on connectivity Non-GBR (Non Guaranteed Bit Rate) Dedicated EPS Bearer Establish in addition when it is needed Can be GBR or non-gbr EPS Bearer 8

9 LTE Resources RB (Resource Block) 12 sub-carriers allocated during a 0.5 ms timeslot are called a resource block A LTE terminal can be allocated a minimum of 2 RBs during 1 subframe (1 ms) Relationship between bandwidth and RB The number of RBs is determined according to bandwidth For example, 6 RBs in 1.4 MHz and 100 RBs in 20 MHz 9

10 Resource Allocation MAC scheduler allocates RBs to UEs Reference: Rohde & Schwarz, UMTS Long Term Evolution (LTE) Technology Introduction 10

11 Important Channel in LTE PDCCH (Physical Downlink Control Channel) Transmit scheduling assignment PDSCH (Physical Downlink Shared Channel) Main data bearing channel which is allocated to users frequency 15 khz 11

12 Downlink Data Transmission Data arrival enb Scheduling UE DL control info. DL data CSI ACK or NACK CSI Channel State Information (CSI) Channel Quality Indicator (CQI), etc. Scheduling Based on CQI HARQ ACK (or NACK) and CSI *HARQ: Hybrid Automatic Retransmission request 12

13 Uplink Data Transmission enb UE SR UL grant BSR Scheduling Data arrival UL data (BSR) (Data arrival) Scheduling Request (SR) Uplink grant Buffer Status Report (BSR) Uplink resource scheduling Uplink data transmission If more uplink data arrives piggybacking BSR 13

14 RRC State Transition RRC_idle Monitor PDCCH According to DRX cycle RRC connection established RRC connection released RRC_connected Connected to Known cell RRC-Idle Monitors a paging channel to detect incoming traffic Performs neighboring cell measurements and cell (re)selection RRC-Connected Transfer of unicast data to/from UE Network controlled mobility such as Handover Performs neighboring cell measurements and reporting Provides channel quality and feedback information 14

15 Random Access Contention-based RA Step 1: Preamble transmission Step 2: Random access response (RAR) includes resource allocation and timing advancement information Step 3: Layer 2 / Layer 3 message Step 4: Contention resolution message 15

16 LTE in ns-3 16

17 LTE-EPC Simulation Model LTE model Supporting the evaluation of the following aspects of LTE systems Radio Resource Management QoS-aware Packet Scheduling Inter-cell Interference Coordination Dynamic Spectrum Access EPC model Supporting the interconnection of multiple UEs to the Internet Packet Data Network (PDN) type: IPv4 SGW/PGW node: functional entities are implemented within a single node Reference: ns-3 Model Library Release ns

18 LTE Protocol Stack PHY model Frequency Division Duplexing (FDD) Granularity Frequency domain: 1 Resource Block (RB) Time domain: 1 Transmission Time Interval (TTI) Supports different frequencies and bandwidths per enbs MAC/Scheduler model Downlink Allocation type 0 (min. scheduling unit = RBG) Round Robin (RR), Proportional Fair (PF), Uplink Only RR supported 18

19 LTE Protocol Stack RLC model Segmentation Reassembly PDCP model Maintenance of PDCP SNs Transfer of SN (Sequence Number) status for handover Unsupported features Header compression/decompression Ciphering/Deciphering 19

20 LTE Protocol Stack LteEnbRrc LtePdcp LteRlc LteEnbMac FfMacScheduler LteEnbPhy 20

21 Overview PHY and channel model architecture Downlink lte-enb-phy.cc lte-ue-phy.cc lte-spectrum-phy.cc multi-model-spectrum-channel.cc 21

22 LTE enb PHY Source code (src/lte/model/lte-enb-phy.cc) Function call flow 1 Frame = 10 Subframe Function of StartSubFrame Process the current burst of control messages Send data frame Trigger the MAC 22

23 Function Flow Downlink Downlink transmission Start 23

24 Function Flow Uplink lte-ue-phy.cc lte-ue-mac.cc StartSubFrame SendLteControlMessage lte-enb-mac.cc ReceiveBsrMessage DoSubframeIndication DoSubframeIndication SendReportBufferStatus DoReceiveLteControlMessage lte-rlc-um.cc DoNotifyTxOpportunity ff-mac-scheduler.cc DoSchedUlCtrlInfoReq DoSchedUlConfigInd DoSchedUlTriggerReq 24

25 Function Flow Random Access lte-ue-phy.cc lte-ue-mac.cc ReceiveLteControlMessageList RecvRaResponse DoSendRachPreamble SendRaPreamble lte-enb-mac.cc DoSubframeIndication RaResponseTimeout lte-rlc-um.cc DoNotifyTxOpportunity ff-mac-scheduler.cc DoSchedDlConfigInd DoSchedDlTriggerReq 25

26 Simulation Examples 26

27 Packet Transmission Example Simulation environment Remote host generates UDP packet Packet size: 1460 bytes Downlink bandwidth: 20 MHz (100 RBs) Internet PGW/SGW enb UE 10 m Remote host UDP client Packet sink 27

28 Simulation Code(1/9) test-lte-epc.cc Define variables NS_LOG_COMPONENT_DEFINE ("TestLteEpc"); using namespace ns3; int main (int argc, char *argv[]) { double ltepktinv = ; // full pumping LTE packet double ltestarttimesec = 1; // application start time double ltestoptimesec = 2; // application end time double downlinkrb = 100; // the number of resource blocks used for downlink 28

29 Simulation Code(2/9) Create node Ipv4GlobalRoutingHelper::PopulateRoutingTables (); NodeContainer remotehostnode, enbnode, uenode; remotehostnode.create (1); enbnode.create (1); uenode.create (1); Create nodes enb node UE node Remote host node 29

30 Simulation Code(3/9) Allocate position Ptr<ListPositionAllocator> positionalloc = CreateObject<ListPositionAllocator> (); positionalloc->add (Vector(0, 0, 0)); // for LTE enb positionalloc->add (Vector(10, 0, 0)); // for LTE UE MobilityHelper mobility; mobility.setpositionallocator (positionalloc); mobility.setmobilitymodel ("ns3::constantpositionmobilitymodel"); mobility.install (enbnode); mobility.install (uenode); 10 m enb node (0, 0, 0) UE node (10, 0, 0) Remote host node 30

31 Simulation Code(4/9) LTE and EPC configuration Using LteHelper and EpcHelper //LteHelper Ptr<LteHelper> ltehelper = CreateObject<LteHelper> (); ltehelper->setattribute ("PathlossModel", StringValue ("ns3::logdistancepropagationlossmodel")); ltehelper->setenbdeviceattribute ("DlBandwidth", UintegerValue (downlinkrb)); ltehelper->setenbdeviceattribute ("UlBandwidth", UintegerValue (downlinkrb)); //EpcHelper Ptr<PointToPointEpcHelper> epchelper = CreateObject<PointToPointEpcHelper> (); ltehelper->setepchelper (epchelper); Ptr<Node> pgw = epchelper->getpgwnode (); //Wired configuration (Remote host and PGW/SGW) PointToPointHelper pointtopoint; pointtopoint.setdeviceattribute ("DataRate", StringValue ("1Gbps")); pointtopoint.setdeviceattribute ("Mtu", UintegerValue (1500)); pointtopoint.setchannelattribute ("Delay", StringValue (" ms")); 10 m Remote host node PGW/SGW enb node (0, 0, 0) UE node (10, 0, 0) 31

32 Assign IP address to EPC Simulation Code(5/9) //Temporal containers NetDeviceContainer p2pdevs, enbdev, uedevs; //Remote host PGW/SGW p2pdevs = pointtopoint.install (remotehostnode.get(0), pgw); enbdev = ltehelper->installenbdevice (enbnode); uedevs = ltehelper->installuedevice (uenode); // IP address assignment for remote host and PGW/SGW InternetStackHelper internet; internet.install (remotehostnode); Ipv4AddressHelper ipv4; ipv4.setbase (" ", " "); Ipv4InterfaceContainer internetipifaces = ipv4.assign (p2pdevs); //Routing setting from EPC to LTE Ipv4StaticRoutingHelper ipv4routinghelper; Ptr<Ipv4StaticRouting> remotehoststaticrouting = ipv4routinghelper.getstaticrouting ((remotehostnode.get(0))->getobject<ipv4> ()); remotehoststaticrouting->addnetworkrouteto (Ipv4Address (" "), Ipv4Mask (" "), 1); 32

33 Assign IP address to LTE //IP address assignment for UE internet.install (uenode); Simulation Code(6/9) Ipv4InterfaceContainer ueifs = epchelper->assignueipv4address (NetDeviceContainer (uedevs)); Ptr<Ipv4StaticRouting> uestaticrouting = ipv4routinghelper.getstaticrouting (uenode.get(0)->getobject<ipv4> ()); uestaticrouting->setdefaultroute (epchelper->getuedefaultgatewayaddress (), 1); // Automatic attachment of a UE device to a suitable cell ltehelper->attach (uedevs.get (0)); Internet PGW/SGW ( ) ( ) enb 10 m UE ( ) Remote host ( ) 33

34 Simulation Code(7/9) Application uint16_t dlport = 10000; //Setting the downlink UDP port ApplicationContainer clientapps; //Making an application container ApplicationContainer serverapps; //Set the destination IP address, port etc. UdpClientHelper dlclienthelper (ueifs.getaddress (0), dlport); dlclienthelper.setattribute ("MaxPackets", UintegerValue ( )); dlclienthelper.setattribute ("Interval", TimeValue (Seconds (ltepktinv))); dlclienthelper.setattribute ("PacketSize", UintegerValue (1460)); //Install the UDP client application to remote server clientapps.add (dlclienthelper.install (remotehostnode.get(0))); //Install the packet sink to UE PacketSinkHelper dlpacketsinkhelper ("ns3::udpsocketfactory", InetSocketAddress (Ipv4Address::GetAny (), dlport)); serverapps.add (dlpacketsinkhelper.install (uenode.get(0))); 34

35 Simulation Code(8/9) Activate dedicated bearer //Setting the Traffic Flow Template (TFT) Ptr<EpcTft> tft = Create<EpcTft> (); EpcTft::PacketFilter dlpf; dlpf.localportstart = dlport; dlpf.localportend = dlport; tft->add (dlpf); //Setting the bearer EpsBearer bearer (EpsBearer::NGBR_VIDEO_TCP_DEFAULT); ltehelper->activatededicatedepsbearer (uedevs.get (0), bearer, tft); Internet PGW/SGW ( ) ( ) enb UE ( ) Remote host UDP client 35 ( ) Packet sink

36 Simulation Code(9/9) Simulation running and Calculate the throughput //Setting the simulation time serverapps.start (Seconds (ltestarttimesec)); clientapps.start (Seconds (ltestarttimesec)); Simulator::Stop (Seconds(lteStopTimeSec)); Simulator::Run (); //Tracing Ptr<PacketSink> sink = serverapps.get (0)->GetObject<PacketSink> (); double ltethroughput = sink->gettotalrx () * 8.0 / ( *(stopTimeSec - ltestarttimesec)); NS_LOG_UNCOND ( UE(" << ueifs.getaddress(0) << ) lte throughput: " << ltethroughput); Simulator::Destroy (); return 0; 36

37 Packet Transmission Examples Simulation Results./waf --run scratch/test-lte-downlink Internet PGW/SGW enb UE Remote host Mbps 37

38 In Class Assignment Make below topology and test throughput test-multicell-skel.cc UE 1 UE 2 10 m 10 m 200 m enb 1 enb 2 interference 99 m 99 m UE m UE m UE 3 UE 4 Solution:./waf --run scratch/test-multicell-sol 38

39 In Class Assignment Uplink transmission test-uplink-skel.cc Internet PGW/SGW enb UE Remote host Uplink transmission Solution:./waf --run scratch/test-uplink-sol 39

40 References 3GPP TS GPP TS The LTE Network Architecture, Alcatel Lucent LTE/EPS overview, NSN ns-3 Model Library Release ns-3.23 E. Dahlman, S. Parkvall, and J. Skold, 4G: LTE/LTE-Advanced for Mobile Broadband, Academic Press, 2011 Rohde & Schwarz, UMTS Long Term Evolution (LTE) Technology Introduction 40

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