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

Ptr< PropagationLossModel >	GetNext ()
	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 ()

virtual	~Object ()

void	AggregateObject (Ptr< Object > other)

void	Dispose (void)
	Run the DoDispose methods of this object and all the objects aggregated to it. More...

AggregateIterator	GetAggregateIterator (void) const

virtual TypeId	GetInstanceTypeId (void) const

template<typename T >
Ptr< T >	GetObject (void) const

template<typename T >
Ptr< T >	GetObject (TypeId tid) const

void	Initialize (void)
	This method calls the virtual DoInitialize method on all the objects aggregated to this object. More...

Public Member Functions inherited from ns3::SimpleRefCount< Object, ObjectBase, ObjectDeleter >
	SimpleRefCount ()
	Constructor. More...

	SimpleRefCount (const SimpleRefCount &o)
	Copy constructor. More...

uint32_t	GetReferenceCount (void) const
	Get the reference count of the object. More...

SimpleRefCount &	operator= (const SimpleRefCount &o)
	Assignment. 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

bool	GetAttributeFailSafe (std::string name, AttributeValue &attribute) const

void	SetAttribute (std::string name, const AttributeValue &value)

bool	SetAttributeFailSafe (std::string name, const AttributeValue &value)

bool	TraceConnect (std::string name, std::string context, const CallbackBase &cb)

bool	TraceConnectWithoutContext (std::string name, const CallbackBase &cb)

bool	TraceDisconnect (std::string name, std::string context, const CallbackBase &cb)

bool	TraceDisconnectWithoutContext (std::string name, const CallbackBase &cb)

Static Public Member Functions
static TypeId	GetTypeId (void)

Static Public Member Functions inherited from ns3::PropagationLossModel
static TypeId	GetTypeId (void)

Static Public Member Functions inherited from ns3::Object
static TypeId	GetTypeId (void)
	Register this type. More...

Static Public Member Functions inherited from ns3::SimpleRefCount< Object, ObjectBase, ObjectDeleter >
static void	Cleanup (void)
	Noop. More...

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

Private Member Functions
	FriisPropagationLossModel (const FriisPropagationLossModel &o)

double	DbmFromW (double w) const

double	DbmToW (double dbm) const

virtual int64_t	DoAssignStreams (int64_t stream)
	Subclasses must implement this; those not using random variables can return zero. More...

virtual double	DoCalcRxPower (double txPowerDbm, Ptr< MobilityModel > a, Ptr< MobilityModel > b) const

FriisPropagationLossModel &	operator= (const FriisPropagationLossModel &o)

Private Attributes
double	m_frequency

double	m_lambda

double	m_minLoss

double	m_systemLoss

Static Private Attributes
static const double	PI = 3.14159265358979323846

Additional Inherited Members
Protected Member Functions inherited from ns3::Object
	Object (const Object &o)

virtual void	DoDispose (void)
	This method is called by Object::Dispose or by the object's destructor, whichever comes first. More...

virtual void	DoInitialize (void)
	This method is called only once by Object::Initialize. More...

virtual void	NotifyNewAggregate (void)
	This method is invoked whenever two sets of objects are aggregated together. More...

Protected Member Functions inherited from ns3::ObjectBase
void	ConstructSelf (const AttributeConstructionList &attributes)

virtual void	NotifyConstructionCompleted (void)
	This method is invoked once all member attributes have been initialized. 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:

: reception power (W)
: transmission power (W)
: transmission gain (unit-less)
: reception gain (unit-less)
$\lambda$ : wavelength (m)
: distance (m)
: 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 , 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 undesireable simulation artifacts.

To avoid these artifact, this implmentation 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:

/ChannelList/[i]/$ns3::WifiChannel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel
/ChannelList/[i]/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel
/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Channel/$ns3::YansWifiChannel/PropagationLossModel/$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.

Definition at line 217 of file propagation-loss-model.h.

Constructor & Destructor Documentation

ns3::FriisPropagationLossModel::FriisPropagationLossModel ( )

Definition at line 171 of file propagation-loss-model.cc.

ns3::FriisPropagationLossModel::FriisPropagationLossModel ( const FriisPropagationLossModel & o )

private

Member Function Documentation

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

private

Definition at line 217 of file propagation-loss-model.cc.

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

private

Definition at line 210 of file propagation-loss-model.cc.

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

privatevirtual

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

Implements ns3::PropagationLossModel.

Definition at line 274 of file propagation-loss-model.cc.

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

privatevirtual

Implements ns3::PropagationLossModel.

Definition at line 224 of file propagation-loss-model.cc.

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

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double ns3::FriisPropagationLossModel::GetFrequency ( void ) const

Returns: the current frequency (Hz)

Definition at line 204 of file propagation-loss-model.cc.

References m_frequency.

Referenced by GetTypeId().

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double ns3::FriisPropagationLossModel::GetMinLoss ( void ) const

Returns: the minimum loss.

Definition at line 190 of file propagation-loss-model.cc.

References m_minLoss.

Referenced by GetTypeId().

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double ns3::FriisPropagationLossModel::GetSystemLoss ( void ) const

Returns: the current system loss (dimension-less)

Definition at line 180 of file propagation-loss-model.cc.

References m_systemLoss.

TypeId ns3::FriisPropagationLossModel::GetTypeId ( void )

static

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

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

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

private

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

Parameters

frequency (Hz)

Set the carrier frequency used in the Friis model calculation.

Definition at line 196 of file propagation-loss-model.cc.

References m_frequency, and m_lambda.

Referenced by GetTypeId().

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void ns3::FriisPropagationLossModel::SetMinLoss ( double minLoss )

Parameters

minLoss the 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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void ns3::FriisPropagationLossModel::SetSystemLoss ( double systemLoss )

Parameters

systemLoss (dimension-less)

Set the system loss used by the Friis propagation model.

Definition at line 175 of file propagation-loss-model.cc.

References m_systemLoss.

Member Data Documentation

double ns3::FriisPropagationLossModel::m_frequency

private

Definition at line 270 of file propagation-loss-model.h.

Referenced by GetFrequency(), and SetFrequency().

double ns3::FriisPropagationLossModel::m_lambda

private

Definition at line 269 of file propagation-loss-model.h.

Referenced by DoCalcRxPower(), and SetFrequency().

double ns3::FriisPropagationLossModel::m_minLoss

private

Definition at line 272 of file propagation-loss-model.h.

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

double ns3::FriisPropagationLossModel::m_systemLoss

private

Definition at line 271 of file propagation-loss-model.h.

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

const double ns3::FriisPropagationLossModel::PI = 3.14159265358979323846

staticprivate

Definition at line 268 of file propagation-loss-model.h.

Referenced by DoCalcRxPower().

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

src/propagation/model/propagation-loss-model.h
src/propagation/model/propagation-loss-model.cc

Public Member Functions

Static Public Member Functions

Private Member Functions

Private Attributes

Static Private Attributes

Additional Inherited Members

Detailed Description

Config Paths

Attributes

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation