1. Session 7. Wireless LAN in ns-3
윤강진
Multimedia & Wireless Networking Laboratory, SNU

2. Contents IEEE 802.11 Wireless LAN Wireless LAN in NS-3 Mobility Model
Example 1
Rate Adaptation Algorithm
NS-3 Structures – Rate Adaptation
Example 2

3. IEEE Wireless LAN

4. IEEE 802.11 Wireless LAN Popular for enterprise, home, “hot-spot”
Enables (indoor) wireless and mobile high-speed networking
“Wireless Ethernet” with comparable speed
Supports up to 600 Mbps within ~100 m range
Runs at unlicensed bands at 2.4 GHz and 5 GHz
Emerging extensions operate at 50~700 MHz (TV white space), 900 MHz, 3.65 GHz (Satellite band), 60 GHz, etc.
MAC and PHY layer technology

5. IEEE 802.11 Standard Overview
Layers 1 and 2
One MAC and multiple PHYs
Application
TCP IP
LLC
MAC
PHY 1 2 3 4 7
Layer
802.11
802.2
2.4 GHz
MAC DS IR FH
.11a OFDM
5 GHz
.11b CCK
.11n OFDM
.11ac OFDM
2.4 & 5 GHz
In 2009
In 2014
5 GHz
In 1999
In 1999
In 2003
.11g OFDM

6. IEEE 802.11 Architecture Infrastructure mode Internet Ad hoc mode
Infrastructure Basic Service Set  BSS
An access point (AP) and multiple stations (STAs)
Every transmission is with AP; no peer-to-peer communication
Ad hoc mode
Independent Basic Service Set  IBSS
Multiple stations (STAs), and no AP
Peer-to-peer communication only
Internet AP
hub, switch
or router AP
BSS 1
BSS 2

7. Layer Interactions
Datagram vs. LPDU vs. MPDU (MAC frame) vs. PPDU (PHY frame)

8. Channels, Association 802.11b/g/n: 2.4GHz-2.485GHz spectrum
13 (in case of Korea) or 11 (in case of Taiwan and USA) channels w/ 5 MHz gap
AP admin chooses frequency for AP
Interference possible: Channel can be same as that chosen by neighboring AP!
STA: Must associate with an AP
Scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address
Selects AP to associate with
May perform authentication
Will typically run DHCP to get IP address in AP’s subnet

9. IEEE : Multiple Access
Avoid collisions: 2+ nodes transmitting at same time
802.11: CSMA - sense before transmitting
Don’t collide with ongoing transmission by other node
802.11: No collision detection!
Difficult to receive (sense collisions) when transmitting due to weak received signals (fading)
Can’t sense all collisions in any case: hidden terminal, fading
Goal: Avoid collisions: CSMA/C(ollision)A(voidance) A B C
A’s signal
strength
space
C’s signal

10. Distributed Coordination Function(DCF)
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
similar to IEEE Ethernet CSMA/CD

11. Enhanced Distributed Channel Access (EDCA)
Prioritized channel access
EDCA queues
Channel access function for each AC
AC_VO > AC_VI > AC_BE > AC_BK

12. Avoiding collisions (more)
idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames
sender first transmits small request-to-send (RTS) packets to BS using CSMA
RTSs may still collide with each other (but they’re short)
BS broadcasts clear-to-send CTS in response to RTS
CTS heard by all nodes
sender transmits data frame
other stations defer transmissions
avoid data frame collisions completely
using small reservation packets!

13. Collision Avoidance: RTS-CTS exchangeB AP
RTS(A)
RTS(B)
reservation collision
RTS(A)
CTS(A)
DATA (A)
ACK(A)
defer
time

14. IEEE 802.11 Frame Format frame seq # duration of reserved
transmission time (RTS/CTS)
frame
control
duration
address 1 2 4 3
payload
CRC 6
seq
Type
From AP
Subtype To
More
frag
WEP
data
Power
mgt
Retry
Rsvd
Protocol
version 2 4 1
frame type
(RTS, CTS, ACK, data)

15. Wireless LAN in NS-3

16. Overview of WiFi Model NS-3 provides models for 802.11
WifiNetDevice models a wireless network interface
NS-3 supports
basic DCF with infrastructure and ad hoc modes
802.11a, b and g physical layers
QoS-based EDCA and queueing extensions of e
various propagation loss models including Nakagami, Rayleigh, Friis, LogDistance, FixedRss, Random
various rate control algorithms including Aarf, Arf, Cara, Onoe, Rraa, ConstantRate, and Minstrel
802.11s (mesh)

17. Overview of WiFi Model Four levels of models PHY layer model
ns3::WifiPhy
MAC low models
ns3::MacLow
Takes care of RTS/CTS/DATA/ACK transmission
ns3::DcfManager, ns3::DcfState
Implements DCF and EDCAF function
ns3::DcaTxop, ns3::EdcaTxopN
Handles packet queue, packet fragmentation, retransmission
MAC high models
ns3::RegularWifiMac
ns3::ApWifiMac, ns3::StaWifiMac, ns3::AdhocWifiMac
Rate control algorithms
ns3::WifiRemoteStationManager

18. Overview of WiFi Model

19. Using the WifiNetDevice
Useful helpers to provide Wifi API
#include <wifi-net-device.h>
Hold together all WiFi-related objects
ns3::WifiChannel
ns3::WifiPhy
ns3::WifiMac
ns3::WifiRemoteStationManager

20. Useful Helpers YansWifiChannelHelper YansWifiPhyHelper
Create a WiFi channel with a default propagation loss and propagation delay model
YansWifiPhyHelper
Create PHY objects appropriate for the YansWifiChannel
NqosWifiMacHelper and QosWifiMacHelper
Create instances of WifiMac
WifiHelper
Create WifiNetDevices including WifiRemoteStationManager, WifiMac, WifiPhy (connected to the WifiChannel)

21. YansWifiChannelHelper
ns3::YansWifiChannelHelper Class Reference
manage and create wifi channel objects for the yans model.
The intent of this class is to make it easy to create a channel object which implements the yans channel model. The yans channel model is described in "Yet Another Network Simulator", 

22. YansWifiPhyHelper ns3::YansWifiPhyHelper Class Reference
Make it easy to create and manage PHY objects for the yans model.
The yans PHY model is described in "Yet Another Network Simulator",
The Pcap and ascii traces generated by the EnableAscii and EnablePcap methods defined in this class correspond to PHY-level traces and come to us via WifiPhyHelper

23. QosWifiMacHelper
Create QoS-enable MAC layers for a ns3::WifiNetDevice

24. NqosWifiMacHelper
Create non QoS-enable MAC layers for a ns3::WifiNetDevice

25. WifiHelper
ns3::WifiHelper::WifiHelper( ) 

26. WiFi PHY Model
The PHY layer implements a single model in the ns3::WifiPhy class
WifiPhy interacts with WifiChannel
PropagationDelayModel
ConstantSpeedPropagationDelayModel
RandomPropagationDelayModel
PropagationLossModel
RandomPropagationLossModel
FriisPropagationLossModel
LogDistancePropagationLossModel
JakesPropagationLossModel
CompositePropagationLossModel
PHY Model is based on the paper [1]
[1] M.Lacage, T.R.Henderson, ”Yet Another Network Simulator,” in Proc. WNS2, Pisa, Italy, 2006.

27. YansWifiChannel ns3::YansWifiChannel Class Reference
#include <yans-wifi-channel.h>
A Yans wifi channel
This wifi channel implements the propagation model described in "Yet Another Network Simulator", (
This class is expected to be used in tandem with the ns3::YansWifiPhy class and contains a ns3::PropagationLossModel and ans3::PropagationDelayModel. By default, no propagation models are set so, it is the caller's responsibility to set them before using the channel.

28. SNIR function over time
YansWifiPhy
ns3::YansWifiPhy Class Reference
#include <yans-wifi-phy.h>
PHY layer model
Attributes
EnergyDetectionThreshold
CcaMode1Threshold
TxGain
RxGain
TxPowerLevels
TxPowerEnd
TxPowerStart
RxNoiseFigure
State
ChannelSwitchDelay
ChannelNumber
SNIR function over time

29. YansWifiPhy
SINR Model in NS-3

30. WiFi MAC Model Following MAC functions are implemented in NS-3
Packet fragmentation and defragmentation
Use of the RTS/CTS
Rate control algorithm
Connection and disconnection to and from an AP
MAC transmission queue
Beacon generation
MSDU aggregation
Block Acknowledgement
etc.
Following MAC functions are not implemented yet
HCCA, TXOP, A-MPDU, Power saving, Handoff, etc.

31. WiFi MAC Model MAC low models MAC high models ns3::MacLow
takes care of RTS/CTS/DATA/ACK transmission
ns3::DcfManager, ns3::DcfState
implements DCF and EDCAF function
ns3::DcaTxop, ns3::EdcaTxopN
handles packet queue, packet fragmentation, retransmission
MAC high models
ns3::RegularWifiMac
handles common MAC operations
ns3::ApWifiMac, ns3::StaWifiMac, ns3::AdhocWifiMac
implements AP, STA, ad hoc MAC

32. MAC Low Models Transmission flow DcaTxop::Queue()
: enqueues a packet in the packet queue
DcfManager::RequestAccess()
: determines whether the channel is busy or not
DcaTxop::NotifyAccessGranted()
: if channel is idle, forwards the packet to MacLow after fragmenting if needed
MacLow::StartTransmission()
: forwards the packet to YansWifiPhy

33. WiFi Transmission Flow

34. WiFi Tx Flow How to transmit a packet (from MAC to PHY)
(Assuming QoS data packet without error)
MAC contains a pointer of PHY (direct access)
Set txVector
using WifiRemoteStationManager
(m_stationManager)
 MacLow has a station pointer
MacLow has a YansWifiPhy pointer

35. YansWifiPhy does not have MacLow pointer
WiFi Rx Flow
How to receive a packet (from PHY to MAC)
(Assuming QoS data packet without error)
PHY does not have a pointer of MAC (callback)
YansWifiPhy does not have MacLow pointer

36. MAC Low Models Reception flow Retransmission flow MacLow::ReceiveOk()
: Schedules ACK or CTS frame, and Callback MacRxMiddle::Receive() when a data packet is received
MacRxMiddle::Receive()
: Forward the packet to the higher MAC after defragmenting if needed
Retransmission flow
MacLow::ReceiveError()
: Calls DcaTxop::MissedAck()
DcaTxop::MissedAck()
: Update backoff and restart channel access request

37. MAC High Models ns3::ApWifiMac ns3::StaWifiMac ns3::AdhocWifiMac
Generates beacon and manages association
Attributes
BeaconInterval
BeaconGeneration
ns3::StaWifiMac
Handles association state
ProbeRequestTimeout
AssocRequestTimeout
MaxMissedBeacons
ActiveProbing
ns3::AdhocWifiMac
Operates without association

38. WifiRemoteStationManager
ns3::WifiRemoteStationManager class
Control the transmission rate and retry counter
Attributes
IsLowLatency
MaxSsrc
MaxSlrc
rtsCtsThreshold
ns3::UintegerValue / uint32_t / 2346
FragmentationThreshold
NonUnicastMode

39. Mobility Model

40. Mobility in NS-3 ns3::MobilityHelper
Helper class used to assign positions and mobility models to nodes
ns3::MobilityHelper::SetPositionAllocator
ns3::MobilityHelper::SetMobilityModel

41. Position Allocator ns3::PositionAllocator Class Reference
Allocate a set of positions. The allocation strategy is implemented in subclasses.
GridPositionAllocator
ListPositionAllocator
RandomBoxPositionAllocator
RandomDiscPositionAllocator
RandomRectanglePositionAllocator
UniformDiscPositionAllocator

42. Mobility Model ConstantAccelerationMobilityModel
ConstantPositionMobilityModel
ConstantVelocityMobilityModel
GaussMarkovMobilityModel
HierarchicalMobilityModel
RandomDirection2dMobilityModel
RandomWalk2dMobilityModel
RandomWaypointMobilityModel
SteadyStateRandomWaypointMobilityModel
WaypointMobilityModel

43. Mobility Usage Example
MobilityHelper mobility; mobility.SetMobilityModel(“ns3::ConstantPositionMobilityModel”); mobility.Install (wifiApNode); wifiApNode.Get(0)->GetObject<MobilityModel>()->SetPosition(Vector(0.0,0.0,0.0)); mobility.SetPositionAllocator(“ns3::RandomDiscPositionAllocator”, “X”, DoubleValue(0.0), “Y”,DoubleValue(0.0), “Rho”, StringValue(“Uniform:0:20”)); mobility.SetMobilityModel(“ns3::RandomWalk2MobilityModel”, “Bounds”, RectangleValue(Rectangle(-50,50,-50,50))); mobility.Install (wifiStaNodes);

44. Example 1

45. Simulation Example Topology
Results with various number of fixed stations in right side
DataRate = 50Mbps
All station use ARF rate adaptation
PacketSize: 200 Bytes, 1000 Bytes
RtsCtsThreshold: 0, 2000 Bytes
All the UDP traffics

46. WiFi Simulation Code (1/4)
#include "ns3/core-module.h" #include "ns3/point-to-point-module.h" #include "ns3/network-module.h" #include "ns3/applications-module.h" #include "ns3/wifi-module.h" #include "ns3/mobility-module.h" #include "ns3/csma-module.h" #include "ns3/internet-module.h" using namespace ns3; NS_LOG_COMPONENT_DEFINE (" session7_ex1"); class MyApp : public Application { public: MyApp (); virtual ~MyApp(); void Setup (Ptr<Socket> socket, Address address, uint32_t packetSize, uint32_t nPackets, DataRate dataRate); private: virtual void StartApplication (void); virtual void StopApplication (void); void ScheduleTx (void); void SendPacket (void); Ptr<Socket> m_socket; Address m_peer; uint32_t m_packetSize; uint32_t m_nPackets; DataRate m_dataRate; EventId m_sendEvent; bool m_running; uint32_t m_packetsSent; };
MyApp::MyApp ()
: m_socket (0),
m_peer (),
m_packetSize (0),
m_nPackets (0),
m_dataRate (0),
m_sendEvent (),
m_running (false),
m_packetsSent (0) { }
MyApp::~MyApp()
m_socket = 0;
void
MyApp::Setup (Ptr<Socket> socket, Address address, uint32_t packetSize, uint32_t nPackets, DataRate dataRate)
m_socket = socket;
m_peer = address;
m_packetSize = packetSize;
m_nPackets = nPackets;
m_dataRate = dataRate;
MyApp::StartApplication (void)
m_running = true;
m_packetsSent = 0;
m_socket->Bind ();
m_socket->Connect (m_peer);
SendPacket ();

47. WiFi Simulation Code (2/4)
void MyApp::StopApplication (void) { m_running = false; if (m_sendEvent.IsRunning ()) Simulator::Cancel (m_sendEvent); } if (m_socket) m_socket->Close (); MyApp::SendPacket (void) Ptr<Packet> packet = Create<Packet> (m_packetSize); m_socket->Send (packet); if (++m_packetsSent < m_nPackets) ScheduleTx (); MyApp::ScheduleTx (void) if (m_running) Time tNext (Seconds (m_packetSize * 8 / static_cast<double> (m_dataRate.GetBitRate ()))); m_sendEvent = Simulator::Schedule (tNext, &MyApp::SendPacket, this); } }
uint32_t data = 0;
static void
RxCnt (Ptr<const Packet> p, const Address &a) {
data = data + p->GetSize();
//NS_LOG_UNCOND (Simulator::Now ().GetSeconds () << "\t" << data); }
int
main (int argc, char *argv[])
int nWifi = 3;
int16_t pktSize=1000;
uint16_t thre=0;
CommandLine cmd;
cmd.AddValue ("nWifi", "Number of wifi STA devices", nWifi);
cmd.AddValue ("pktSize", "Size of UDP packet", pktSize);
cmd.AddValue ("thre", "RTC/CTS threshold", thre);
cmd.Parse (argc,argv);
NodeContainer wifiStaNodes;
wifiStaNodes.Create (nWifi);
NodeContainer wifiApNode;
wifiApNode.Create (1);

48. WiFi Simulation Code (3/4)
YansWifiChannelHelper channel = YansWifiChannelHelper::Default (); YansWifiPhyHelper phy = YansWifiPhyHelper::Default (); phy.SetChannel (channel.Create ()); WifiHelper wifi = WifiHelper::Default (); wifi.SetRemoteStationManager ("ns3::ArfWifiManager", "RtsCtsThreshold", UintegerValue (thre) ); NqosWifiMacHelper mac = NqosWifiMacHelper::Default (); Ssid ssid = Ssid ("ns-3-ssid"); mac.SetType ("ns3::StaWifiMac", "Ssid", SsidValue (ssid), "ActiveProbing", BooleanValue (false)); NetDeviceContainer staDevices; staDevices = wifi.Install (phy, mac, wifiStaNodes); mac.SetType ("ns3::ApWifiMac", "Ssid", SsidValue (ssid)); NetDeviceContainer apDevices; apDevices = wifi.Install (phy, mac, wifiApNode); MobilityHelper mobility; mobility.SetMobilityModel (ns3::ConstantPositionMobilityModel"); mobility.Install (wifiStaNodes); mobility.Install (wifiApNode);
for ( int i = 0; i<nWifi; i++){
wifiStaNodes.Get(i)->GetObject<MobilityModel>()
->SetPosition(Vector( (i>0)*5.0 + i*5.0, 0.0, 0.0)); }
InternetStackHelper stack;
stack.Install (wifiApNode);
stack.Install (wifiStaNodes);
Ipv4AddressHelper address;
address.SetBase (" ", " ");
Ipv4InterfaceContainer wifiApInterface;
Ipv4InterfaceContainer wifiStaInterfaces;
wifiApInterface = address.Assign (apDevices);
wifiStaInterfaces = address.Assign (staDevices);
uint16_t port = 20803;

49. WiFi Simulation Code (4/4)
PacketSinkHelper udpsink ("ns3::UdpSocketFactory", Address (InetSocketAddress (Ipv4Address::GetAny (), port))); ApplicationContainer udpapp = udpsink.Install (wifiApNode.Get (0)); udpapp.Start (Seconds (0.0)); udpapp.Stop (Seconds (7.0)); Ptr<Socket> udpsocket[5]; Ptr<MyApp> udpflow[5] = CreateObject<MyApp> (); for (int j = 0; j < nWifi ; j++){ udpsocket[j] = Socket::CreateSocket (wifiStaNodes.Get (j), UdpSocketFactory::GetTypeId ()); udpflow[j] ->Setup (udpsocket[j], Address (InetSocketAddress (wifiApInterface.GetAddress (0), port)), pktSize, , DataRate ("50Mbps")); wifiStaNodes.Get (j)->AddApplication (udpflow[j]); udpflow[j]->SetStartTime (Seconds (1.0)); udpflow[j]->SetStopTime (Seconds (6.0)); } Ipv4GlobalRoutingHelper::PopulateRoutingTables (); udpapp.Get(0)->TraceConnectWithoutContext ("Rx", MakeCallback(&RxCnt)); Simulator::Stop (Seconds (7.0)); phy.EnablePcap (" session5_ex2 ", apDevices.Get (0)); Simulator::Run (); Simulator::Destroy (); NS_LOG_UNCOND("#. of STAs= " << nWifi << ", PacketSize= "<< pktSize << ", RtsCtsThreshold= "<< thre << " => Throughput= "<< (double)data*8/1000/1000/5 <<"Mbps");

50. Simulation Example
Simulation result

51. Rate Adaptation Algorithm

52. How to Select the Rate? Modulation and Coding Scheme (MCS)
Modulation type: BPSK, QPSK, 16-QAM, 64-QAM,…
Coding rate: 1/2, 3/4, 2/3, 5/6, ...
E.g., n (w/ 20 MHz channel and 800 ns guard interval)
MCS index
Tx rate (Mbps)
Modulation
Coding Rate
6.5
BPSK
1/2 1 13
QPSK 2
19.5
3/4 3 26
16-QAM 4 39 5 52
64-QAM
2/3 6
58.5 7 65
5/6

53. Rate Adaptation Adapts the MCS for varying SNR
Efficiency vs. Robustness tradeoff
Higher rate can transmit faster at the cost of lower reliability
Fading, shadowing, and mobility make the channel variation

54. How to Know the Channel Condition?
Loss-based (sampling) rate adaptation
Open loop approach
# of successful transmission, loss statistics, …
ARF, AARF, CARA, SampleRate, and RRAA
SNR-based rate adaptation
Closed or open loop approach
Measured SNR
RBAR and CHARM

55. ARF Algorithm (1/2)
Auto Rate Fallback (ARF) is the first commercial implementation that exploits multi-rate capability
Senders use history of previous transmission error rates to select future transmission rates
If no errors, increase the data rate
If errors, decrease the data rate
Achieves performance gain over plain

56. ARF Algorithm (2/2)
If two consecutive ACK frames are not received correctly, the second retry and subsequent transmissions are done at a lower rate and a timer is started
When the number of successfully received ACKs reaches 10 or the timer goes off, a probe frame is sent at the next higher rate
However, if an ACK is NOT received for this frame, the rate is lowered back and the timer is restarted

57. AARF Algorithm Problem of ARF The essence of Adaptive ARF (AARF)
ARF tries constantly (every 10 successfully transmitted consecutive packet) to use a higher rate to be able to channel condition changes
The essence of Adaptive ARF (AARF)
To avoid the scenario described above, AARF increases the threshold used to decide when to increase the current rate from 10 to 20, 40, 80
When the probing packet fails, it switches back immediately to the previous lower rate, but it also multiplies by two the number of consecutive successful transmissions required to switch to a higher rate

58. ARF vs. AARF

59. Channel Error vs. Collision Error
Solution for the channel error
The transmitter should decrease the transmission rate
Solution for the collision error
The transmitter should not decrease the rate upon collision losses
Decreasing rate increases the collision probability!
We need a scheme to handle this collision errors

60. CARA Algorithm Procedure of Collision Aware Rate Adaptation (CARA)
ARF-based rate adaptation
Data frame transmitted without RTS/CTS
If the transmission fails, RTS/CTS exchange is activated for the next retransmission
If this retransmission fails, then the rate is lowered
Transmission failure after RTS/CTS must be due to channel errors
If retransmission is successful, stay at same rate and send next frame without RTS/CTS

61. ARF vs. CARA

62. RRAA Algorithm Robust Rate Adaptation Algorithm (RRAA) Goals
Improve the throughput performance
Robust against various dynamics
Three components:
Loss estimation
Rate change
Adaptive RTS filter

63. Loss Estimation
Instead of single probe frame, RRAA uses a loss estimation window and computes the estimated loss ratio over the window
Uses upper and lower loss threshold for each rate and estimated loss ratio to decide when to switch rates

64. Adaptive RTS Filter Selective use of RTS/CTS. RTSwindow (RTSwnd)
Window is increased by one when last frame lost without RTS (potentially due to a collision)
When the last frame was lost with RTS or succeeded without RTS, RTSwnd is halved (assume no collision involved)

65. Receiver-Based AutoRate (RBAR) Algorithm
Not compliant
Receivers control sender’s transmission rate
RTS and CTS are modified to contain the information on size and rate
Uses analysis of RTS reception (RSSI) to estimate SNR and send choice back to sender in CTS
Receiver picks rate based on a priori SNR thresholds

66. SNR-Based Rate Adaptation
Who measure the SNR of the link?
RTS/CTS: RBAR
ACK
Channel reciprocity
Who select the transmission rate?
The transmitter
The receiver

67. NS-3 Structures – Rate Adaptation

68. Rate Selection WifiTxVector class TxVector in 802.11 Consists of,
Transmission PHY rate
Transmission power level
The maximum number of retransmission
Guard interval index
Number of stream
Number of stream in beamforming
STBC index
Managed in WifiRemoteStationManager

69. Rate Selection WifiRemoteStationManager
Each station has its own station manager
Manages txVector based on MacLow
Default: ARF
Others
AARF, AMRR, CARA
Minstrel, Onoe, RRAA
Constant, Ideal

70. Rate Selection Flow of getting transmission rate
SendDataPacket (void) in MacLow
Calls GetDataTxVector (m_currentPacket, &m_currentHdr) in MacLow
m_stationManager->GetDataTxVector (to, hdr, packet, size) in WifiRemoteStationManager
Whenever WifiRemoteStationManager receives the transmission result of a packet, it updates rate parameter based on designated algorithm
Success: ReportDataOk (…)
 increase the transmission PHY rate for next packet possibly (m_rate++)
Failure: ReportDataFailed (…)
 decrease the transmission PHY rate for next packet possibly (m_rate--)

71. Rate Adaptation in NS-3
Wifi Model provides a set of Rate control algorithms
ns3::ArfWifiManager
ns3::AarfcdWifiManager
ns3::AarfWifiManager
ns3::AmrrWifiManager
ns3::CaraWifiManager
ns3::RraaWifiManager
ns3::IdealWifiManager
ns3::OnoeWifiManager
ns3::MinstrelWifiManager
ns3::ConstantRateWifiManager
In this lecture, we use some rate adaptation schemes

72. ARF Rate Control Algorithm
Ns3::ArfWifiManager
This implementation differs from the initial description in that it uses a packet-based timer rather than a time-based timer
Attributes
Config::SetDefault (“ns3::ArfWifiManager::TimerThreshold”, UintegerValue (15));
TimerThreshold: The 'timer' threshold in the ARF algorithm.
Set with class: ns3::UintegerValue
Underlying type: uint32_t 0:
Initial value: 15
SuccessThreshold: The minimum number of sucessfull transmissions to try a new rate.
Initial value: 10

73. AARF Rate Control Algorithm
Ns3::AarfWifiManager
Attributes
Config::SetDefault (“ns3::AarfWifiManager::SuccessK, DoubleValue (2));
SuccessK: Multiplication factor for the success threshold in the AARF algorithm.
Set with class: ns3::DoubleValue
Initial value: 2
TimerK: Multiplication factor for the timer threshold in the AARF algorithm.
MaxSuccessThreshold: Maximum value of the success threshold in the AARF algorithm.
Set with class: ns3::UintegerValue
Initial value: 60

74. Attributes for AARF Attributes
MinTimerThreshold: The minimum value for the 'timer' threshold in the AARF algorithm.
Set with class: ns3::UintegerValue
Initial value: 15
MinSuccessThreshold: The minimum value for the success threshold in the AARF algorithm.
Initial value: 10

75. CARA Rate Control Algorithm
ns3::CaraWifiManager
Attributes
Config::SetDefault (“ns3::CaraWifiManager::ProbeThreshold”, UintegerValue (1));
ProbeThreshold: The number of consecutive transmissions failure to activate the RTS probe.
Set with class: ns3::UintegerValue
Initial value: 1
FailureThreshold: The number of consecutive transmissions failure to decrease the rate.
Initial value: 2
SuccessThreshold: The minimum number of successfull transmissions to try a new rate.
Initial value: 10
Timeout: The 'timer' in the CARA algorithm
Initial value: 15

76. ns3::MinstrelWifiManager
Chooses the best rate based on loss statistics
Popular rate control algorithm
Bug fix
Current problem: globally uses a variable “m_nsupported” which indicates the number of supported rates
Should fix to use individually

77. Ideal Rate Control Algorithm
SNR-based rate adaptation
An 'ideal' rate control algorithm similar to RBAR in spirit
Every station keeps track of the signal-to-noise ratio (SNR) of every packet received and sends back this SNR to the original transmitter by an out-of-band mechanism
Each transmitter keeps track of the last SNR sent back by a receiver and uses it to pick a transmission mode based on a set of SNR thresholds built from a target Bit Error Rate (BER) and transmission mode-specific SNR/BER curves

78. ns3::IdealWifiManager
Attributes
Config::SetDefault (“ns3::IdealWifiManager::BerThreshold”, DoubleValue (1e-05));
BerThreshold: The maximum Bit Error Rate acceptable at any transmission mode
Set with class: ns3::DoubleValue
Underlying type: double e+308: e+308
Initial value: 1e-05

79. Wifi Channel Wifi Channel Helper YansWifiChannelHelper Static channel
YansWifiPhyHelper wifiPhy = YansWifiPhyHelper::Default ();
YansWifiChannelHelper wifiChannel;
wifiChannel.SetPropagationDelay ("ns3::ConstantSpeedPropagationDelayModel");
Static channel
wifiChannel.AddPropagationLoss ("ns3::LogDistancePropagationLossModel");
Dynamic channel
wifiChannel.AddPropagationLoss ("ns3::JakesPropagationLossModel");
Config::SetDefault ("ns3::JakesPropagationLossModel::DopplerFreq", DoubleValue(1));
Channel setting
wifiPhy.SetChannel (wifiChannel.Create ());

80. Static Channel Log distance propagation loss model
Path loss without Rayleigh fading
wifiChannel.AddPropagationLoss ("ns3::LogDistancePropagationLossModel");

81. Dynamic Channel Log distance model + jakes models
Path loss with Rayleigh fading
wifiChannel.AddPropagationLoss ("ns3:: JakesPropagationLossModel ");
Config::SetDefault ("ns3::JakesPropagationLossModel::DopplerFreq", DoubleValue(1));

82. Optimal Rate Selection
JakesPropagationLossModel
Doppler velocity 1.0 m/s
LogDistancePropagationLossModel
Pathloss exponent 4

83. Rate Adaptation Setting
Wifi Helper
WifiHelper wifi;
wifi.SetRemoteStationManager ("ns3::ArfWifiManager");
wifi.SetRemoteStationManager ("ns3::AarfWifiManager");
wifi.SetRemoteStationManager ("ns3::CaraWifiManager");
wifi.SetRemoteStationManager ("ns3::RraaWifiManager");
wifi.SetRemoteStationManager ("ns3::IdealWifiManager");

84. Mobility Model Mobility Helper MobilityHelper mobility;
Ptr<ListPositionAllocator> positionAlloc = CreateObject<ListPositionAllocator> ();
positionAlloc->Add (Vector (0.0, 0.0, 0.0));
positionAlloc->Add (Vector (30.0, 0.0, 0.0));
mobility.SetPositionAllocator (positionAlloc);
mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
mobility.Install (c);

85. Example 2

86. Simulation Example Topology
Results with various number of fixed stations in right side
DataRate = 25 Mbps
All station use ARF, AARF, CARA, Ideal rate adaptation
PacketSize: 200 Bytes, 1000 Bytes
RtsCtsThreshold: 1500 Bytes
All the UDP traffics

87. WiFi Simulation Code (1/3)
#include <string> #include <iostream> #include <fstream> #include "ns3/core-module.h" #include "ns3/point-to-point-module.h" #include "ns3/network-module.h" #include "ns3/applications-module.h" #include "ns3/wifi-module.h" #include "ns3/mobility-module.h" #include "ns3/csma-module.h" #include "ns3/internet-module.h" using namespace ns3; uint32_t data=0; static void RxCnt (Ptr<const Packet> p, const Address &a) { data = data + p->GetSize(); //NS_LOG_UNCOND (Simulator::Now ().GetSeconds () << "\t" << data); }
void
PrintResults(char *fout, int nSta, int ra_idx, double thpt) {
std::ofstream out;
out.open(fout,std::ios::app);
out << std::fixed;
out << std::showpoint;
out.precision(6);
out << "nSta\t" << nSta << "\traIndex\t" << ra_idx << "\tthpt\t" << thpt << "\tMbps" << std::endl;
out.close(); }
char fout[255];
int main (int argc, char *argv[])
int nSta = 1;
int ra_idx = 0;
std::string raName;
CommandLine cmd;
cmd.AddValue("nSTA", "number of stations", nSta);
cmd.AddValue("ra_idx", "rate adaptation algorithm index", ra_idx);
cmd.Parse (argc, argv);
sprintf(fout, "./raIdx_%d.txt", ra_idx);
NodeContainer ApNode;
ApNode.Create (1);
NodeContainer StaNodes;
StaNodes.Create (nSta);
NodeContainer c;
c.Add (ApNode);
c.Add (StaNodes);

88. WiFi Simulation Code (2/3)
WifiHelper wifi; wifi.SetStandard (WIFI_PHY_STANDARD_80211a); YansWifiPhyHelper wifiPhy = YansWifiPhyHelper::Default (); wifiPhy.SetPcapDataLinkType (YansWifiPhyHelper::DLT_IEEE802_11_RADIO); YansWifiChannelHelper wifiChannel ; wifiChannel.SetPropagationDelay ("ns3::ConstantSpeedPropagationDelayModel"); wifiChannel.AddPropagationLoss ("ns3::JakesPropagationLossModel"); wifiChannel.AddPropagationLoss ("ns3::LogDistancePropagationLossModel"); Config::SetDefault("ns3::JakesProcess::DopplerFrequencyHz", DoubleValue(50/3)); wifiPhy.SetChannel (wifiChannel.Create ()); switch(ra_idx) { case 0: raName = "ARF"; wifi.SetRemoteStationManager ("ns3::ArfWifiManager"); break; case 1: raName = "AARF"; wifi.SetRemoteStationManager ("ns3::AarfWifiManager"); break;
case 2
raName = "CARA"; wifi.SetRemoteStationManager ("ns3::CaraWifiManager");
break;
case 3:
raName = "IDEAL"; wifi.SetRemoteStationManager ("ns3::IdealWifiManager");
default:
NS_LOG_UNCOND("Invalid rate idx"); }
NqosWifiMacHelper wifiMac = NqosWifiMacHelper::Default ();
Ssid ssid = Ssid ("wifi-default");
wifiMac.SetType ("ns3::StaWifiMac","Ssid", SsidValue (ssid), "ActiveProbing", BooleanValue (false));
NetDeviceContainer staDevice = wifi.Install (wifiPhy, wifiMac, StaNodes);
wifiMac.SetType ("ns3::ApWifiMac", "Ssid", SsidValue (ssid));
NetDeviceContainer apDevice = wifi.Install (wifiPhy, wifiMac, ApNode.Get(0));
NetDeviceContainer devices;
devices.Add (apDevice);
devices.Add (staDevice);
MobilityHelper mobility;

89. WiFi Simulation Code (3/3)
Ptr<ListPositionAllocator> positionAlloc = CreateObject<ListPositionAllocator> (); positionAlloc->Add (Vector (0.0, 0.0, 0.0)); positionAlloc->Add (Vector (30.0, 0.0, 0.0)); positionAlloc->Add (Vector (0.0, 30.0, 0.0)); positionAlloc->Add (Vector (-30.0, 0.0, 0.0)); positionAlloc->Add (Vector (0.0, -30.0, 0.0)); positionAlloc->Add (Vector (0.0, 0.0, 30.0)); mobility.SetPositionAllocator (positionAlloc); mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel"); mobility.Install (c); InternetStackHelper internet; internet.Install (c); Ipv4AddressHelper ipv4; ipv4.SetBase (" ", " "); ipv4.Assign (devices); uint16_t port = 9; PacketSinkHelper sink ("ns3::UdpSocketFactory", Address (InetSocketAddress (Ipv4Address::GetAny (), port)));
ApplicationContainer app;
app = sink.Install (ApNode.Get (0));
app.Start (Seconds (0.0));
app.Get(0)->TraceConnectWithoutContext ("Rx", MakeCallback(&RxCnt));
OnOffHelper onoff ("ns3::UdpSocketFactory", Address (InetSocketAddress (Ipv4Address (" "), port)));
onoff.SetAttribute ("OnTime", StringValue("ns3::ConstantRandomVariable[Constant=1]"));
onoff.SetAttribute ("OffTime", StringValue("ns3::ConstantRandomVariable[Constant=0]"));
onoff.SetAttribute ("DataRate", StringValue ("25Mbps"));
onoff.SetAttribute ("PacketSize", UintegerValue (1500));
for(int i=0; i<nSta; i++) {
app = onoff.Install (StaNodes.Get (i));
app.Start (Seconds (1.0));
app.Stop (Seconds (3.0)); }
wifiPhy.SetPcapDataLinkType(YansWifiPhyHelper::DLT_IEEE802_11_RADIO);
wifiPhy.EnablePcap ("session7_ex2", devices);
Simulator::Stop (Seconds (3.5));
Simulator::Run ();
Simulator::Destroy ();
NS_LOG_UNCOND( raName << " " << "nSta" << nSta<< " "<< (double)data*8/1000/1000/2 << " Mbps");
PrintResults(fout, nSta, ra_idx, (double)data*8/1000/1000/2);
return 0;

90. Simulation Example
Simulation result

91. In-class Assignment Topology
Make the topology with wireless topology helpers like below
Make results with various number of fixed stations
Each UDP traffic rate = 50 Mbps
Destination of all traffic is AP
All stations use ARF or CARA rate adaptation
We want to see the total throughput as the number of UDP generators (STA) varies in various simulation environment
Simulation environment (9 possible combinations)
PacketSize: 200, 1000, and 2000 Bytes
RtsCtsThreshold (in ARF): 0, 2000 Bytes

92. References
Computer Networking: A Top Down Approach 5th edition, Jim Kurose, Keith Ross, Addison-Wesley, April, 2009
NS-3 Doxygen,
NS-3 manual,
NS-3 tutorial,

93. References
A. Kamerman and L. Monteban, “WaveLAN-II: A High-Performance Wireless LAN for the Unlicensed Band,” Bell Lab Technical Journal, Vol. 2, No. 3, pp , 1997.
M. Lacage, M.H. Manshaei, and T. Turletti, “IEEE Rate Adaptation: A Practical Approach,” in Proc. ACM MSWiM, Venezia, Italy, Oct
J. Kim, S. Kim, S. Choi, and D. Qiao, "CARA: Collision-Aware Rate Adaptation for IEEE WLANs," in Proc. IEEE INFOCOM, Barcelona, Spain, April 2006.
S. H. Y. Wong, H. Yang, S. Lu, and V. Bharghavan, “Robust rate adaptation for wireless networks,” in Proc. ACM MobiCom, Los Angeles, California, USA, Sep
G. Holland, N. Vaidya, and P. Bahl, “A Rate-Adaptive MAC Protocol for Multihop Wireless Networks,” in Proc. ACM MobiCom, Rome, Italy, July 2001.

94. Thank You !