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

FriisPropagationLossModel &	operator= (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< PropagationLossModel >	GetNext ()
	Gets the next PropagationLossModel in the chain of loss models that act on the signal.

PropagationLossModel &	operator= (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< Object >	GetObject () 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< Object >	GetObject (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.

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.

SimpleRefCount &	operator= (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) 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.

virtual TypeId	GetInstanceTypeId () const =0
	Get the most derived TypeId for this Object.

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

Additional Inherited Members
virtual int64_t	DoAssignStreams (int64_t stream)=0
	Assign a fixed random variable stream number to the random variables used by this model.

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.

Related Functions inherited from ns3::ObjectBase
static TypeId	GetObjectIid ()
	Ensure the TypeId for ObjectBase gets fully configured to anchor the inheritance tree properly.

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 $ 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]/$ns3::WifiNetDevice/Channel/$ns3::SpectrumChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Channel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Phy/Channel/$ns3::SpectrumChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Phy/Channel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Phys/[i]/Channel/$ns3::SpectrumChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Phys/[i]/Channel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::FriisPropagationLossModel"
"/NodeList/[i]/DeviceList/[i]/$ns3::LrWpanNetDevice/Channel/PropagationLossModel/$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: constructwriteread
MinLoss: The minimum value (dB) of the total loss, used at short ranges.
- Set with class: ns3::DoubleValue
- Underlying type: double -1.79769e+308:1.79769e+308
- Initial value: 0
- Flags: constructwriteread
SystemLoss: The system loss
- Set with class: ns3::DoubleValue
- Underlying type: double -1.79769e+308:1.79769e+308
- Initial value: 1
- Flags: constructwriteread

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

Definition at line 252 of file propagation-loss-model.h.

Constructor & Destructor Documentation

◆ FriisPropagationLossModel() [1/2]

ns3::FriisPropagationLossModel::FriisPropagationLossModel ( )

Definition at line 177 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

w	the Watt value

Returns: the Dbm

Definition at line 227 of file propagation-loss-model.cc.

◆ DbmToW()

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

private

Transforms a Dbm value to Watt.

Parameters

dbm	the Dbm value

Returns: the Watts

Definition at line 220 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

stream first stream index to use

Returns: the number of stream indices assigned by this model

Implements ns3::PropagationLossModel.

Definition at line 285 of file propagation-loss-model.cc.

◆ DoCalcRxPower()

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

overrideprivatevirtual

PropagationLossModel.

Parameters

txPowerDbm	current transmission power (in dBm)
a	the mobility model of the source
b	the mobility model of the destination

Returns: the reception power after adding/multiplying propagation loss (in dBm)

Implements ns3::PropagationLossModel.

Definition at line 234 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 214 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 200 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 (dimension-less)

Definition at line 188 of file propagation-loss-model.cc.

References m_systemLoss.

◆ GetTypeId()

TypeId ns3::FriisPropagationLossModel::GetTypeId ( )

static

Get the type ID.

Returns: the object TypeId

Definition at line 149 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 & )

delete

◆ SetFrequency()

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

Parameters

frequency (Hz)

Set the carrier frequency used in the Friis model calculation.

Definition at line 206 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

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 194 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 182 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 323 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 322 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 325 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 324 of file propagation-loss-model.h.

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

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

Additional Inherited Members

Detailed Description

Config Paths

Attributes

Constructor & Destructor Documentation

◆ FriisPropagationLossModel() [1/2]

◆ FriisPropagationLossModel() [2/2]

Member Function Documentation

◆ DbmFromW()

◆ DbmToW()

◆ DoAssignStreams()

◆ DoCalcRxPower()

◆ GetFrequency()

◆ GetMinLoss()

◆ GetSystemLoss()

◆ GetTypeId()

◆ operator=()

◆ SetFrequency()

◆ SetMinLoss()

◆ SetSystemLoss()

Member Data Documentation

◆ m_frequency

◆ m_lambda

◆ m_minLoss

◆ m_systemLoss