1. Session 8. LTE in ns-3
박태준
Multimedia & Wireless Networking Laboratory, SNU

2. Contents LTE Overview LTE in ns-3 Simulation Examples
Packet Transmission Example
Configurable Parameters
Multi-cell Environment Example

3. LTE Overview

4. 3GPP LTE and LTE-A LTE (Long Term Evolution) LTE-A (LTE Advanced)
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

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

6. Key Entity eNB (evolved Node B) MME (Mobility Management Entity)
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

7. Protocol Architecture

8. QoS and EPS Bearer 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

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

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

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
15 kHz
frequency

12. LTE in ns-3

13. 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-3.22

14. LTE Protocol Stack PHY model MAC/Scheduler 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

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

16. Simulation Examples

17. Simulation Code Flow LteHelper EpcHelper Install eNB and UE
Attach UE to eNB
EpcHelper
Attach eNB to EPC
Activate default bearer
Get P-GW node in order for LTE network to connect external network
Single node in ns-3

18. LteHelper Install LTE eNB/UE protocol stack to a set of node
NetDeviceContainer InstallEnbDevice (NodeContainer c)
NetDeviceContainer InstallUeDevice (NodeContainer c)
Attach UE(s) to eNB(s)
Automatic attachment of UE(s)
void Attach (Ptr<NetDevice> ueDevice)
void Attach (NetDeviceContainer ueDevices)
Manual attachment of UE(s)
void Attach (NetDeviceContainer ueDevices, Ptr<NetDevice> enbDevice)
void Attach (Ptr<NetDevice> ueDevice, Ptr<NetDevice> enbDevice)

19. LteHelper Set scheduler type Set DL/UL bandwidth
void LteHelper::SetSchedulerType(std::string type)
Type
Round Robin: RrFfMacScheduler
Proportional Fair: PfFfMacScheduler …
Set DL/UL bandwidth
DL bandwidth:
Void LteHelper::SetEnbDeviceAttribute(“DlBandwidth”, UintegerValue())
UL bandwidth
Void LteHelper::SetEnbDeviceAttribute(“UlBandwidth”, UintegerValue())

20. EpcHelper Attach eNB to EPC Activate default bearer Get P-GW node
Automatically attachment of eNB(s) to an EPC
Related functions of LteHelper
void LteHelper::SetEpcHelper (Ptr<EpcHelper> h)
NetDeviceContainer LteHelper::InstallEnbDevice (NodeContainer c)
Activate default bearer
Automatically activate default bearer for each UE
Related function of LteHelper
void LteHelper::Attach( … )
Get P-GW node
Ptr<Node> GetPgwNode ()

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

22. 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

23. Simulation Code(2/9) Create nodes UE node eNB node Remote host node
Ipv4GlobalRoutingHelper::PopulateRoutingTables ();
NodeContainer remoteHostNode, enbNode, ueNode;
remoteHostNode.Create (1);
enbNode.Create (1);
ueNode.Create (1);
Create nodes
UE node
eNB node
Remote host node

24. Simulation Code(3/9) eNB node UE node Remote host node
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

25. Simulation Code(4/9) eNB node UE node Remote host node PGW/SGW
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"));
eNB node
(0, 0, 0)
UE node
(10, 0, 0)
Remote host node
10 m
PGW/SGW

26. Simulation Code(5/9) Assign IP address to EPC //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);

27. Simulation Code(6/9) PGW/SGW eNB UE Remote host
Assign IP address to LTE
//IP address assignment for UE
internet.Install (ueNode);
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));
10 m UE
eNB
PGW/SGW
Internet
Remote host
( )
( )
( )
( )

28. 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)));

29. Simulation Code(8/9) PGW/SGW eNB UE Remote host
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); UE
eNB
PGW/SGW
Internet
Remote host
( )
( )
( )
( )
Packet sink
UDP client

30. 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;

31. Packet Transmission Examples
Simulation Results
./waf --run scratch/test-lte-epc UE
eNB
PGW/SGW
Internet
Remote host
69.87 Mbps

32. Configurable Parameters
Simulation environment
Which factor affect throughput performance?
Example
eNB UE
10 m
100 m
100 RBs
50 RBs
1 ms inter-packet interval
2 ms inter-packet interval
10 MHz bandwidth
20 MHz bandwidth
Transmission power
Center frequency

33. Configurable Parameters
eNB transmission power configuration
test-lte-epc-config-skeleton.cc
double ltePktInv = ;
double downlinkRb = 100;
double dlEarfcn = 100;
double lteTxPower = 30;
double distance = 10;
CommandLine cmd;
cmd.AddValue ("dlEarfcn", "downlink frequency",dlEarfcn);
cmd.AddValue ("lteTxPower", "lte eNB transmission power [dBm]",lteTxPower);
cmd.Parse (argc, argv);
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetEnbDeviceAttribute ("DlEarfcn", UintegerValue (dlEarfcn));
lteHelper->SetEnbDeviceAttribute ("UlEarfcn", UintegerValue (dlEarfcn+18000));
Config::SetDefault("ns3::LteEnbPhy::TxPower", DoubleValue (lteTxPower));

34. Configurable Parameters
In class assignment
test-lte-epc-config-skeleton.cc
double ltePktInv = ;
double downlinkRb = 100;
double dlEarfcn = 100;
double lteTxPower = 30;
double distance = 10;
CommandLine cmd;
// To Do List
// Insert command line to get the number of resource blocks used for downlink
// Insert command line to get the distance between eNB and UE
// Insert command line to get the LTE packet interval
cmd.AddValue ("dlEarfcn", "downlink frequency",dlEarfcn);
cmd.AddValue ("lteTxPower", "lte eNB transmission power [dBm]",lteTxPower);
cmd.Parse (argc, argv);

35. Configurable Parameters
test-lte-epc-config.cc
Bandwidth configuration
double ltePktInv = ;
double downlinkRb = 100;
double dlEarfcn = 100;
double ulEarfcn = 18100;
double lteTxPower = 30;
double distance = 10;
CommandLine cmd;
cmd.AddValue ("downlinkRb", "number of resource blocks in downlink",downlinkRb);
cmd.AddValue ("distance", “distance between eNB and UE [m]",distance);
cmd.AddValue ("ltePktInv", “packet generation interval of UDP [s]",ltePktInv);
cmd.AddValue ("dlEarfcn", "downlink frequency",dlEarfcn);
cmd.AddValue ("lteTxPower", "lte eNB transmission power [dBm]",lteTxPower);
cmd.Parse (argc, argv);

36. Configurable Parameters
Distance between eNB and UE configuration
LTE packet interval configuration

37. Multi-cell Environment Example
Simulation environment
eNB 1
eNB 2
UE 1
UE 2
UE 6
UE 5
interference
UE 3
UE 4
10 m
10 m
200 m
99 m
99 m
100 m
100 m

38. Multi-cell Environment Example
Simulation code (scratch/test-multicell-skeleton.cc)
Make topology
Attaching eNB 1 to UE 1, 3, 5 and eNB 2 to UE 2, 4, 6
Ptr<ListPositionAllocator> positionAlloc = CreateObject<ListPositionAllocator> ();
positionAlloc->Add (Vector(-100.0, 0.0, 0.0)); //for enb 1
positionAlloc->Add (Vector(100.0, 0.0, 0.0)); //for enb 2
positionAlloc->Add (Vector(-100.0, 10.0, 0.0)); //for ue 1
positionAlloc->Add (Vector(100.0, 10.0, 0.0)); //for ue 2
positionAlloc->Add (Vector(-100.0, , 0.0)); //for ue 3
positionAlloc->Add (Vector(100.0, , 0.0)); //for ue 4
positionAlloc->Add (Vector(-1.0, 0.0, 0.0)); //for ue 5
positionAlloc->Add (Vector(1.0, 0.0, 0.0)); //for ue 6
MobilityHelper mobility;
mobility.SetMobilityModel("ns3::ConstantPositionMobilityModel");
mobility.SetPositionAllocator(positionAlloc);
mobility.Install(enbNodes);
mobility.Install(ueNodes);
for (uint16_t i = 0; i < numberOfNodes; i++) {
lteHelper->Attach (ueLteDevs.Get(i), enbLteDevs.Get(i));
lteHelper->Attach (ueLteDevs.Get(i+2), enbLteDevs.Get(i));
lteHelper->Attach (ueLteDevs.Get(i+4), enbLteDevs.Get(i)); }

39. Multi-cell Environment Example
Simulation code (scratch/test-multicell-skeleton.cc)
Install and start applications on UEs
Throughput calculation
uint16_t dlPort = 1234;
ApplicationContainer clientApps;
ApplicationContainer serverApps;
for (uint32_t u = 0; u < ueNodes.GetN (); ++u) {
PacketSinkHelper dlPacketSinkHelper ("ns3::UdpSocketFactory", InetSocketAddress (Ipv4Address::GetAny (), dlPort + u));
serverApps.Add (dlPacketSinkHelper.Install (ueNodes.Get(u)));
UdpClientHelper dlClientHelper (ueIpIface.GetAddress (u), dlPort + u);
dlClientHelper.SetAttribute ("Interval", TimeValue (MilliSeconds(interPacketInterval)));
dlClientHelper.SetAttribute ("MaxPackets", UintegerValue( ));
clientApps.Add (dlClientHelper.Install (remoteHostNode.Get(0))); }
Ptr<PacketSink> sink = serverApps.Get (0) -> GetObject<PacketSink> ();
NS_LOG_UNCOND("LTE throughput :" << sink->GetTotalRx()*8.0 / << " Mbps");

40. Multi-cell Environment Example
Simulation results
./waf --run scratch/test-multicell
eNB 1
eNB 2
UE 1
UE 2
UE 6
UE 5
interference
UE 3
UE 4
10 m
100 m
99 m
200 m
6.2 Mbps
1.7 Mbps
0.8 Mbps

41. References 3GPP TS 36.300 3GPP TS 36.104
The LTE Network Architecture, Alcatel Lucent
LTE/EPS overview, NSN
ns-3 Model Library Release ns-3.22
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

42. Thank You !