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ns3::FriisPropagationLossModel Class Reference

a Friis propagation loss model More...

#include "propagation-loss-model.h"

+ Inheritance diagram for ns3::FriisPropagationLossModel:
+ Collaboration diagram for ns3::FriisPropagationLossModel:

Public Member Functions

 FriisPropagationLossModel ()
 
double GetFrequency (void) const
 
double GetMinLoss (void) const
 
double GetSystemLoss (void) const
 
void SetFrequency (double frequency)
 
void SetMinLoss (double minLoss)
 
void SetSystemLoss (double systemLoss)
 
- Public Member Functions inherited from ns3::PropagationLossModel
 PropagationLossModel ()
 
virtual ~PropagationLossModel ()
 
int64_t AssignStreams (int64_t stream)
 If this loss model uses objects of type RandomVariableStream, set the stream numbers to the integers starting with the offset 'stream'. More...
 
double CalcRxPower (double txPowerDbm, Ptr< MobilityModel > a, Ptr< MobilityModel > b) const
 Returns the Rx Power taking into account all the PropagationLossModel(s) chained to the current one. More...
 
Ptr< PropagationLossModelGetNext ()
 Gets the next PropagationLossModel in the chain of loss models that act on the signal. More...
 
void SetNext (Ptr< PropagationLossModel > next)
 Enables a chain of loss models to act on the signal. More...
 
- Public Member Functions inherited from ns3::Object
 Object ()
 Constructor. More...
 
virtual ~Object ()
 Destructor. More...
 
void AggregateObject (Ptr< Object > other)
 Aggregate two Objects together. More...
 
void Dispose (void)
 Dispose of this Object. More...
 
AggregateIterator GetAggregateIterator (void) const
 Get an iterator to the Objects aggregated to this one. More...
 
virtual TypeId GetInstanceTypeId (void) const
 Get the most derived TypeId for this Object. More...
 
template<>
Ptr< ObjectGetObject () const
 Specialization of () for objects of type ns3::Object. More...
 
template<typename T >
Ptr< T > GetObject (TypeId tid) const
 Get a pointer to the requested aggregated Object by TypeId. More...
 
template<>
Ptr< ObjectGetObject (TypeId tid) const
 Specialization of (TypeId tid) for objects of type ns3::Object. More...
 
template<typename T >
Ptr< T > GetObject (void) const
 Get a pointer to the requested aggregated Object. More...
 
void Initialize (void)
 Invoke DoInitialize on all Objects aggregated to this one. More...
 
bool IsInitialized (void) const
 Check if the object has been initialized. More...
 
- Public Member Functions inherited from ns3::SimpleRefCount< Object, ObjectBase, ObjectDeleter >
 SimpleRefCount ()
 Default constructor. More...
 
 SimpleRefCount (const SimpleRefCount &o)
 Copy constructor. More...
 
uint32_t GetReferenceCount (void) const
 Get the reference count of the object. More...
 
SimpleRefCountoperator= (const SimpleRefCount &o)
 Assignment operator. More...
 
void Ref (void) const
 Increment the reference count. More...
 
void Unref (void) const
 Decrement the reference count. More...
 
- Public Member Functions inherited from ns3::ObjectBase
virtual ~ObjectBase ()
 Virtual destructor. More...
 
void GetAttribute (std::string name, AttributeValue &value) const
 Get the value of an attribute, raising fatal errors if unsuccessful. More...
 
bool GetAttributeFailSafe (std::string name, AttributeValue &value) const
 Get the value of an attribute without raising erros. More...
 
void SetAttribute (std::string name, const AttributeValue &value)
 Set a single attribute, raising fatal errors if unsuccessful. More...
 
bool SetAttributeFailSafe (std::string name, const AttributeValue &value)
 Set a single attribute without raising errors. More...
 
bool TraceConnect (std::string name, std::string context, const CallbackBase &cb)
 Connect a TraceSource to a Callback with a context. More...
 
bool TraceConnectWithoutContext (std::string name, const CallbackBase &cb)
 Connect a TraceSource to a Callback without a context. More...
 
bool TraceDisconnect (std::string name, std::string context, const CallbackBase &cb)
 Disconnect from a TraceSource a Callback previously connected with a context. More...
 
bool TraceDisconnectWithoutContext (std::string name, const CallbackBase &cb)
 Disconnect from a TraceSource a Callback previously connected without a context. More...
 

Static Public Member Functions

static TypeId GetTypeId (void)
 Get the type ID. More...
 
- Static Public Member Functions inherited from ns3::PropagationLossModel
static TypeId GetTypeId (void)
 Get the type ID. More...
 
- Static Public Member Functions inherited from ns3::Object
static TypeId GetTypeId (void)
 Register this type. More...
 
- Static Public Member Functions inherited from ns3::ObjectBase
static TypeId GetTypeId (void)
 Get the type ID. More...
 

Private Member Functions

 FriisPropagationLossModel (const FriisPropagationLossModel &)
 Copy constructor. More...
 
double DbmFromW (double w) const
 Transforms a Watt value to Dbm. More...
 
double DbmToW (double dbm) const
 Transforms a Dbm value to Watt. More...
 
int64_t DoAssignStreams (int64_t stream) override
 Subclasses must implement this; those not using random variables can return zero. More...
 
double DoCalcRxPower (double txPowerDbm, Ptr< MobilityModel > a, Ptr< MobilityModel > b) const override
 Returns the Rx Power taking into account only the particular PropagationLossModel. More...
 
FriisPropagationLossModeloperator= (const FriisPropagationLossModel &)
 Copy constructor. More...
 

Private Attributes

double m_frequency
 the carrier frequency More...
 
double m_lambda
 the carrier wavelength More...
 
double m_minLoss
 the minimum loss More...
 
double m_systemLoss
 the system loss More...
 

Additional Inherited Members

- Protected Member Functions inherited from ns3::Object
 Object (const Object &o)
 Copy an Object. More...
 
virtual void DoDispose (void)
 Destructor implementation. More...
 
virtual void DoInitialize (void)
 Initialize() implementation. More...
 
virtual void NotifyNewAggregate (void)
 Notify all Objects aggregated to this one of a new Object being aggregated. More...
 
- Protected Member Functions inherited from ns3::ObjectBase
void ConstructSelf (const AttributeConstructionList &attributes)
 Complete construction of ObjectBase; invoked by derived classes. More...
 
virtual void NotifyConstructionCompleted (void)
 Notifier called once the ObjectBase is fully constructed. More...
 

Detailed Description

a Friis propagation loss model

The Friis propagation loss model was first described in "A Note on a Simple Transmission Formula", by "Harald T. Friis".

The original equation was described as: $ \frac{P_r}{P_t} = \frac{A_r A_t}{d^2\lambda^2} $ with the following equation for the case of an isotropic antenna with no heat loss: $ A_{isotr.} = \frac{\lambda^2}{4\pi} $

The final equation becomes: $ \frac{P_r}{P_t} = \frac{\lambda^2}{(4 \pi d)^2} $

Modern extensions to this original equation are: $ P_r = \frac{P_t G_t G_r \lambda^2}{(4 \pi d)^2 L}$

With:

  • $ P_r $ : reception power (W)
  • $ P_t $ : transmission power (W)
  • $ G_t $ : transmission gain (unit-less)
  • $ G_r $ : reception gain (unit-less)
  • $ \lambda $ : wavelength (m)
  • $ d $ : distance (m)
  • $ L $ : system loss (unit-less)

In the implementation, $ \lambda $ is calculated as $ \frac{C}{f} $, where $ C = 299792458$ m/s is the speed of light in vacuum, and $ f $ is the frequency in Hz which can be configured by the user via the Frequency attribute.

The Friis model is valid only for propagation in free space within the so-called far field region, which can be considered approximately as the region for $ d > 3 \lambda $. The model will still return a value for $ d < 3 \lambda $, as doing so (rather than triggering a fatal error) is practical for many simulation scenarios. However, we stress that the values obtained in such conditions shall not be considered realistic.

Related with this issue, we note that the Friis formula is undefined for $ d = 0 $, and results in $ P_r > P_t $ for $ d < \lambda / 2 \sqrt{\pi} $. Both these conditions occur outside of the far field region, so in principle the Friis model shall not be used in these conditions. In practice, however, Friis is often used in scenarios where accurate propagation modeling is not deemed important, and values of $ d = 0 $ can occur. To allow practical use of the model in such scenarios, we have to 1) return some value for $ d = 0 $, and 2) avoid large discontinuities in propagation loss values (which could lead to artifacts such as bogus capture effects which are much worse than inaccurate propagation loss values). The two issues are conflicting, as, according to the Friis formula, $\lim_{d \to 0 } P_r = +\infty $; so if, for $ d = 0 $, we use a fixed loss value, we end up with an infinitely large discontinuity, which as we discussed can cause undesirable simulation artifacts.

To avoid these artifact, this implementation of the Friis model provides an attribute called MinLoss which allows to specify the minimum total loss (in dB) returned by the model. This is used in such a way that $ P_r $ continuously increases for $ d \to 0 $, until MinLoss is reached, and then stay constant; this allow to return a value for $ d = 0 $ and at the same time avoid discontinuities. The model won't be much realistic, but at least the simulation artifacts discussed before are avoided. The default value of MinLoss is 0 dB, which means that by default the model will return $ P_r = P_t $ for $ d <= \lambda / 2 \sqrt{\pi} $. We note that this value of $ d $ is outside of the far field region, hence the validity of the model in the far field region is not affected.

Config Paths

ns3::FriisPropagationLossModel is accessible through the following paths with Config::Set and Config::Connect:

  • "/NodeList/[i]/DeviceList/[i]/$ns3::LrWpanNetDevice/Channel/PropagationLossModel/$ns3::FriisPropagationLossModel"
  • "/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Channel/$ns3::SpectrumChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
  • "/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Channel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
  • "/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/Channel/$ns3::SpectrumChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
  • "/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/Channel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
  • "/ChannelList/[i]/$ns3::SpectrumChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
  • "/ChannelList/[i]/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"

Attributes

  • Frequency: The carrier frequency (in Hz) at which propagation occurs (default is 5.15 GHz).
    • Set with class: ns3::DoubleValue
    • Underlying type: double -1.79769e+308:1.79769e+308
    • Initial value: 5.15e+09
    • Flags: construct write read
  • SystemLoss: The system loss
    • Set with class: ns3::DoubleValue
    • Underlying type: double -1.79769e+308:1.79769e+308
    • Initial value: 1
    • Flags: construct write read
  • MinLoss: The minimum value (dB) of the total loss, used at short ranges. Note:
    • Set with class: ns3::DoubleValue
    • Underlying type: double -1.79769e+308:1.79769e+308
    • Initial value: 0
    • Flags: construct write read

No TraceSources are defined for this type.
Size of this type is 72 bytes (on a 64-bit architecture).

Definition at line 267 of file propagation-loss-model.h.

Constructor & Destructor Documentation

◆ FriisPropagationLossModel() [1/2]

ns3::FriisPropagationLossModel::FriisPropagationLossModel ( )

Definition at line 172 of file propagation-loss-model.cc.

◆ FriisPropagationLossModel() [2/2]

ns3::FriisPropagationLossModel::FriisPropagationLossModel ( const FriisPropagationLossModel )
private

Copy constructor.

Defined and unimplemented to avoid misuse

Member Function Documentation

◆ DbmFromW()

double ns3::FriisPropagationLossModel::DbmFromW ( double  w) const
private

Transforms a Watt value to Dbm.

Parameters
wthe Watt value
Returns
the Dbm

Definition at line 218 of file propagation-loss-model.cc.

◆ DbmToW()

double ns3::FriisPropagationLossModel::DbmToW ( double  dbm) const
private

Transforms a Dbm value to Watt.

Parameters
dbmthe Dbm value
Returns
the Watts

Definition at line 211 of file propagation-loss-model.cc.

◆ DoAssignStreams()

int64_t ns3::FriisPropagationLossModel::DoAssignStreams ( int64_t  stream)
overrideprivatevirtual

Subclasses must implement this; those not using random variables can return zero.

Parameters
streamthe stream index offset start
Returns
the number of stream indices assigned by this model

Implements ns3::PropagationLossModel.

Definition at line 275 of file propagation-loss-model.cc.

◆ DoCalcRxPower()

double ns3::FriisPropagationLossModel::DoCalcRxPower ( double  txPowerDbm,
Ptr< MobilityModel a,
Ptr< MobilityModel b 
) const
overrideprivatevirtual

Returns the Rx Power taking into account only the particular PropagationLossModel.

Parameters
txPowerDbmcurrent transmission power (in dBm)
athe mobility model of the source
bthe mobility model of the destination
Returns
the reception power after adding/multiplying propagation loss (in dBm)

Implements ns3::PropagationLossModel.

Definition at line 225 of file propagation-loss-model.cc.

References ns3::MobilityModel::GetDistanceFrom(), m_lambda, m_minLoss, m_systemLoss, max, NS_LOG_DEBUG, and NS_LOG_WARN.

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◆ GetFrequency()

double ns3::FriisPropagationLossModel::GetFrequency ( void  ) const
Returns
the current frequency (Hz)

Definition at line 205 of file propagation-loss-model.cc.

References m_frequency.

Referenced by GetTypeId().

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◆ GetMinLoss()

double ns3::FriisPropagationLossModel::GetMinLoss ( void  ) const
Returns
the minimum loss.

Definition at line 191 of file propagation-loss-model.cc.

References m_minLoss.

Referenced by GetTypeId().

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◆ GetSystemLoss()

double ns3::FriisPropagationLossModel::GetSystemLoss ( void  ) const
Returns
the current system loss (dimension-less)

Definition at line 181 of file propagation-loss-model.cc.

References m_systemLoss.

◆ GetTypeId()

TypeId ns3::FriisPropagationLossModel::GetTypeId ( void  )
static

Get the type ID.

Returns
the object TypeId

Definition at line 146 of file propagation-loss-model.cc.

References GetFrequency(), GetMinLoss(), m_systemLoss, ns3::MakeDoubleAccessor(), SetFrequency(), SetMinLoss(), and ns3::TypeId::SetParent().

Referenced by ns3::LteHelper::GetTypeId().

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◆ operator=()

FriisPropagationLossModel& ns3::FriisPropagationLossModel::operator= ( const FriisPropagationLossModel )
private

Copy constructor.

Defined and unimplemented to avoid misuse

Returns

◆ SetFrequency()

void ns3::FriisPropagationLossModel::SetFrequency ( double  frequency)
Parameters
frequency(Hz)

Set the carrier frequency used in the Friis model calculation.

Definition at line 197 of file propagation-loss-model.cc.

References m_frequency, and m_lambda.

Referenced by Bug2843TestCase::DoRun(), SpectrumWifiPhyFilterTest::DoSetup(), TestDlOfdmaPhyTransmission::DoSetup(), TestUlOfdmaPpduUid::DoSetup(), TestUlOfdmaPhyTransmission::DoSetup(), TestPhyPaddingExclusion::DoSetup(), and GetTypeId().

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◆ SetMinLoss()

void ns3::FriisPropagationLossModel::SetMinLoss ( double  minLoss)
Parameters
minLossthe minimum loss (dB)

no matter how short the distance, the total propagation loss (in dB) will always be greater or equal than this value

Definition at line 186 of file propagation-loss-model.cc.

References m_minLoss.

Referenced by GetTypeId().

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◆ SetSystemLoss()

void ns3::FriisPropagationLossModel::SetSystemLoss ( double  systemLoss)
Parameters
systemLoss(dimension-less)

Set the system loss used by the Friis propagation model.

Definition at line 176 of file propagation-loss-model.cc.

References m_systemLoss.

Member Data Documentation

◆ m_frequency

double ns3::FriisPropagationLossModel::m_frequency
private

the carrier frequency

Definition at line 347 of file propagation-loss-model.h.

Referenced by GetFrequency(), and SetFrequency().

◆ m_lambda

double ns3::FriisPropagationLossModel::m_lambda
private

the carrier wavelength

Definition at line 346 of file propagation-loss-model.h.

Referenced by DoCalcRxPower(), and SetFrequency().

◆ m_minLoss

double ns3::FriisPropagationLossModel::m_minLoss
private

the minimum loss

Definition at line 349 of file propagation-loss-model.h.

Referenced by DoCalcRxPower(), GetMinLoss(), and SetMinLoss().

◆ m_systemLoss

double ns3::FriisPropagationLossModel::m_systemLoss
private

the system loss

Definition at line 348 of file propagation-loss-model.h.

Referenced by DoCalcRxPower(), GetSystemLoss(), GetTypeId(), and SetSystemLoss().


The documentation for this class was generated from the following files: