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

Static Public Member Functions

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

Private Member Functions

double DbmFromW (double w) const
 Transforms a Watt value to Dbm.
 
double DbmToW (double dbm) const
 Transforms a Dbm value to Watt.
 
int64_t DoAssignStreams (int64_t stream) override
 Assign a fixed random variable stream number to the random variables used by this model.
 
double DoCalcRxPower (double txPowerDbm, Ptr< MobilityModel > a, Ptr< MobilityModel > b) const override
 PropagationLossModel.
 

Private Attributes

double m_frequency
 the carrier frequency
 
double m_lambda
 the carrier wavelength
 
double m_minLoss
 the minimum loss
 
double m_systemLoss
 the system loss (linear factor)
 

Additional Inherited Members

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

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.

Definition at line 241 of file propagation-loss-model.h.

Constructor & Destructor Documentation

◆ FriisPropagationLossModel() [1/2]

ns3::FriisPropagationLossModel::FriisPropagationLossModel ( )

Definition at line 167 of file propagation-loss-model.cc.

◆ FriisPropagationLossModel() [2/2]

ns3::FriisPropagationLossModel::FriisPropagationLossModel ( const FriisPropagationLossModel & )
delete

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

Assign a fixed random variable stream number to the random variables used by this model.

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

Parameters
streamfirst stream index to use
Returns
the number of stream indices assigned by this model

Implements ns3::PropagationLossModel.

Definition at line 276 of file propagation-loss-model.cc.

◆ DoCalcRxPower()

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

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 m_lambda, m_minLoss, m_systemLoss, NS_LOG_DEBUG, and NS_LOG_WARN.

◆ GetFrequency()

double ns3::FriisPropagationLossModel::GetFrequency ( ) 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 ( ) 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 ( ) const
Returns
the current system loss (linear factor, dimension-less)

Definition at line 179 of file propagation-loss-model.cc.

References m_systemLoss.

Referenced by GetTypeId().

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◆ GetTypeId()

TypeId ns3::FriisPropagationLossModel::GetTypeId ( )
static

Get the type ID.

Returns
the object TypeId

Definition at line 138 of file propagation-loss-model.cc.

References GetFrequency(), GetMinLoss(), GetSystemLoss(), ns3::MakeDoubleAccessor(), ns3::MakeDoubleChecker(), SetFrequency(), SetMinLoss(), ns3::TypeId::SetParent(), and SetSystemLoss().

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

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◆ operator=()

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

◆ 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 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 185 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(linear factor, dimension-less)

Set the system loss used by the Friis propagation model. Value should be greater than or equal to 1; the default of 1 corresponds to no system loss.

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

References m_systemLoss, and NS_ABORT_MSG_UNLESS.

Referenced by GetTypeId().

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Member Data Documentation

◆ m_frequency

double ns3::FriisPropagationLossModel::m_frequency
private

the carrier frequency

Definition at line 314 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 313 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 316 of file propagation-loss-model.h.

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

◆ m_systemLoss

double ns3::FriisPropagationLossModel::m_systemLoss
private

the system loss (linear factor)

Definition at line 315 of file propagation-loss-model.h.

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


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