mimo::WSSUSChannel2 Class Reference

#include <wssuschannel2.h>

Inheritance diagram for mimo::WSSUSChannel2:

[legend]List of all members.


Public Member Functions
	WSSUSChannel2 (int deviceID, DeviceSystemIntf *system, const simth::PropertyList &pl, double maxDelay, double max_doppler)
virtual	~WSSUSChannel2 ()
	destructor
virtual void	refresh ()
void	getTransfer (int relative_time, MatrixFreqSignal &trans) const
void	transmit (const VectorTimeSignal &insym, VectorTimeSignal &outsym)
void	setRiceFactor (double rf)
void	setRiceFactor_dB (double rf)
void	setTimeNormalization (unsigned duration=0)
void	setFreqNormalization (double freqDist, int numFreqs, unsigned duration=0)
virtual void	startOfSimulation ()
virtual void	print (std::ostream &os) const
Protected Types
typedef std::vector< ScattererParam >	ScatVect
	Container type for all scatterer parameters.
typedef std::vector< PathParam >	PathVect
	Container type for all path parameters.
Protected Member Functions
int	roundTimeToSamples (double value) const
	Function for rounding delay times into number of samples.
virtual double	diceNewDelay () const =0
virtual double	diceNewPhase () const =0
virtual double	diceNewAmpl () const
virtual double	diceNewAoA () const
virtual double	diceNewAoD () const
void	getImpulseResponse (int relative_time, MatrixTimeSignal &t, int increment_time=0) const
Protected Attributes
unsigned	num_paths
double	max_delay
	maximal delay time
double	max_doppler
	Maximum doppler frequency.
unsigned	L_T
	Number of transmit scatterers.
unsigned	L_R
	Number of receive scatterers.
unsigned	paths_per_scatterer
ScatVect	scatterers_tx
	Transmit scatterer data.
CMatrix	steering_tx
	Transmit steering matrix, calculated from the scatterer data.
CMatrix	doppler_tx
ScatVect	scatterers_rx
	Receive scatterer data.
CMatrix	steering_rx
	Receive steering matrix, calculated from the scatterer data.
CMatrix	doppler_rx
PathVect	h_pathparams
	The path parameters.
CMatrixSeq::storage_type	h_paths
AntennaArray *	array_geometry_tx
	Geometry of the tx antenna array.
AntennaArray *	array_geometry_rx
	Geometry of the rx antenna array.
double	delta_t
	Sampling time of the sequences to be transmitted.
VectorTimeSignal::storage_type	prevsym
	previously transmitted samples of one OFDM symbol
bool	firstSequence
MatrixTimeSignal::storage_type	imp_resp
	The matrix-valued impulse response of this channel.
MatrixFreqSignal::storage_type	cacheTransfer
int	cacheTime
	Time for which the cached transfer function was valid.
bool	isTransferCacheValid
bool	timevariant
	Whether this channel is time variant at all.
int	current_time
	The current time in samples.
Related Functions
(Note that these are not member functions.)
	propertylist_WSSUSChannel2 (not_a_function)
Classes
class	PathParam
class	ScattererParam

Detailed Description

WSSUS Channel.

This is the abstract base class of statistical time-variant multipath MIMO channel models for mobile radio environments. The time-variant MIMO impulse response is modelled by $K$ independent paths which are determined according to given probability density functions (pdf).

For each propagation path $k$ the following parameters are randomly determined: delay $\tau_k$ (e.g. with a negative exponential pdf), Doppler frequency $f_{Dk}$ (e.g. with a Jakes pdf), initial phase $\theta_k$ (e.g. with a uniform pdf), and angle of arrival $\alpha_k$ and departure $\beta_k$ (e.g. with discrete set of uniformly distributed values).

Additionally, a geometry of the antenna array on transmitter and receiver side is chosen by WSSUSChannel2::setArrayGeometry(). With the chosen array geometry, the phase shift at each individual transmitter antenna $m$ and receiver antenna $n$ can be calculated as a function of the angles of arrival $\phi_n(\alpha_k)$ and departure $\psi_m(\beta_k)$ .

The impulse response of the channel from antenna $m$ to antenna $n$ is

$h_{nm}(\tau,t) = \frac{1}{\sqrt{K}} \sum_{k=1}^{K} e^{j(\theta_k +2\pi f_{Dk}t)} \cdot \delta(\tau - \tau_k) \cdot e^{j[\phi_n(\alpha_k)+\psi_m(\beta_k)]}$

(LaTeX rules!)

The realizations of these parameters are chosen randomly in WSSUSChannel2::refresh(). Each individial parameter is obtained independently from each other through the purely virtual functions diceNewDelay() and diceNewPhase(). These virtual functions are implemented in a derived class, which is responsible for choosing the PDFs of each parameter.

The angles of arrival and departure (functions diceNewAoA() and diceNewAoD()) are an exception. They are already implemented in WSSUSChannel2 class because otherwise the random number generators are not properly resetted upon refresh(). The probability distribution behind these variables is a bit tricky: The realizations for the angles are not uniformly distributed! Instead, for these random variables at each refresh() a small set of discrete angles is drawn from a uniform distribution. Then, each path angle is drawn from this small set of discrete angles. This means that many paths will have the same angle -- and this effect is desired in order to model the fact of a small number of "angles of arrival", which is commonly agreed upon in the MIMO community.

Various types of specialized channels can be supported by derived classes. These classes complement this general channel model (WSSUSChannel2) with special pdf's (one example is given above).

There are two derived channel models which can be constructed for a given coherence time and coherence bandwidth and for a given maximal Doppler frequency and maximal delay, respectively. For the WSSUS channel there are functions which modify the channel's coherence time or bandwidth.

Furthermore, there are the following four COST channel models which can be selected with a different constructor: RA (rural area) -- $0.7\mu s$ maximal delay, TU (typical urban) -- $7\mu s$ max. delay, BU (bad urban) -- $10\mu s$ max. delay, HT (hilly terrain) -- $20\mu s$ max. delay

Author:: Christian Stimming <stimming@tuhh.de> but the non-%MIMO parts are heavily copied from Peter Haase and others.

Member Typedef Documentation

typedef std::vector<ScattererParam> mimo::WSSUSChannel2::ScatVect [protected]

Container type for all scatterer parameters.

typedef std::vector<PathParam> mimo::WSSUSChannel2::PathVect [protected]

Container type for all path parameters.

Constructor & Destructor Documentation

mimo::WSSUSChannel2::WSSUSChannel2 ( int deviceID,

DeviceSystemIntf * system,

const simth::PropertyList & pl,

double maxDelay,

double max_doppler

)

Constructor for given maximal delay and Doppler frequency. (FIXME: These are rather specified in the derived class, aren't they?)

Parameters:

deviceID Device ID

system The parent system

pl The list of properties this device has. It needs to have the properties "nr_tx", "nr_rx" set.

maxDelay Maximal delay of the channel. The negative exponential pdf of the delay is modified according to the given value so that longer delays do not occur.

max_doppler The maximum doppler frequency.

virtual mimo::WSSUSChannel2::~WSSUSChannel2 ( ) [virtual]

destructor

Member Function Documentation

int mimo::WSSUSChannel2::roundTimeToSamples ( double value ) const [inline, protected]

Function for rounding delay times into number of samples.

virtual double mimo::WSSUSChannel2::diceNewDelay ( ) const [protected, pure virtual]

Returns a new realization of the delay random variable. To be implemented by a derived class.
Implemented in mimo::WSSUSChannel2ExpDelay.

virtual double mimo::WSSUSChannel2::diceNewPhase ( ) const [protected, pure virtual]

Returns a new realization of the initial phase random variable. Well, this already kind of implies this random variable should follow a uniform distribution in $[0\ldots2\pi[$ .
To be implemented by a derived class.
Implemented in mimo::WSSUSChannel2JakesUniform.

virtual double mimo::WSSUSChannel2::diceNewAmpl ( ) const [protected, virtual]

Returns a new realization of the amplitudes of the phases. May or may not be implemented by a derived class. The default implementation returns one, or, if the property "path_ampl_random" is true, it returns a Rayleigh distributed random variate.

virtual double mimo::WSSUSChannel2::diceNewAoA ( ) const [protected, virtual]

Returns a new realization of the angles of arrival random variable. We already have an implementation of this function here because otherwise the RNG is not properly resetted upon refresh().

virtual double mimo::WSSUSChannel2::diceNewAoD ( ) const [protected, virtual]

Returns a new realization of the angles of departure random variable. We already have an implementation of this function here because otherwise the RNG is not properly resetted upon refresh().

virtual void mimo::WSSUSChannel2::refresh ( ) [virtual]

Calculate new random paths.
For each propagation path $k$ the following parameters are randomly determined: delay $\tau_k$ (e.g. with a negative exponential pdf), Doppler frequency $f_{Dk}$ (e.g. with a Jakes pdf), initial phase $\theta_k$ (e.g. with a uniform pdf), and angle of arrival $\alpha_k$ and departure $\beta_k$ . In other words, all parameters in the MIMO::PathParam class.
Additionally, a geometry of the antenna array on transmitter and receiver side is chosen by WSSUSChannel2::setArrayGeometry(). With the chosen array geometry, the phase shift at each individual transmitter antenna $m$ and receiver antenna $n$ can be calculated as a function of the angles of arrival $\phi_n(\alpha_k)$ and departure $\psi_m(\beta_k)$ .
Note: If you want new PDFs to be used, it is sufficient to create a derived class with different diceNewDelay() and diceNewPhase() (also for angles of arrival/departure). However, these functions all imply that the PDFs are independent of each other. If you want some joint PDFs, then of course you need to fully reimplement this function and no longer only the independent functions mentioned before.
Reimplemented from simth::Device.

void mimo::WSSUSChannel2::getTransfer ( int relative_time,

MatrixFreqSignal & trans

) const [virtual]

Determines channel transfer factors.
An ideal estimation of the channel transfer function is performed. This means, the exact values $H(f_i,t_0)$ are determined, where $t_0$ is ${\tt relative_time} * {\tt delta\_t}$ and $f_i = n\cdot \mbox{\tt delta\_f}, n=0, \dots, \mbox{\tt num\_f}-1$ .
NOTE: The time argument is a relative time. time = 0 indicates the transmission time of the last sample transmitted, i.e. the sample that has "just been transmitted" over the channel. For example time = -numSamples would indicate the transmission time of the first sample of the last transmitted sequence.

Parameters:

relative_time The relative time at which the transfer function is calculated. This is relative to the last time sample that was transmitted over this channel!

trans The FreqSignal that receives the resulting transfer function. It needs to have a proper delta_f attribute set.

Implements mimo::MIMOChannel.

void mimo::WSSUSChannel2::transmit ( const VectorTimeSignal & insym,

VectorTimeSignal & outsym

) [virtual]

Transmits a symbol sequence.
The symbol sequence insym is transmitted over the channel with the result outsym. Inter-symbol interference of a previously transmitted sequence is considered.
Implements mimo::MIMOChannel.

void mimo::WSSUSChannel2::setRiceFactor ( double rf )

Sets the Ricean factor of the channel, default is 0

void mimo::WSSUSChannel2::setRiceFactor_dB ( double rf )

sets the Ricean factor of the channel (in dB), default is $-\infty$

void mimo::WSSUSChannel2::setTimeNormalization ( unsigned duration = 0 )

Sets the normalization mode to TIME.

void mimo::WSSUSChannel2::setFreqNormalization ( double freqDist,

int numFreqs,

unsigned duration = 0

)

Sets the normalization mode to FREQ. freqDist and numFreqs are used to specify the used frequency range (starts by zero).

virtual void mimo::WSSUSChannel2::startOfSimulation ( ) [virtual]

Called by the simulation system in the beginning of each simulation run.
Reimplemented from mimo::MIMOChannel.

virtual void mimo::WSSUSChannel2::print ( std::ostream & os ) const [virtual]

Reimplemented from mimo::MIMOChannel.

void mimo::WSSUSChannel2::getImpulseResponse ( int relative_time,

MatrixTimeSignal & t,

int increment_time = 0

) const [protected]

Friends And Related Function Documentation

propertylist_WSSUSChannel2 ( not_a_function ) [related]

These are the properties of class WSSUSChannel2 . This list is auto-generated from the XML-Devicelist of this device by means of an XSLT transformation script.
Description of this device in the XML file: This MIMO channel uses the WSSUS2 channel model and extends it to the MIMO case by multiplying the path coefficients with the appropriate steering vectors.
Additionally, this Device calculates the actual transmission either in time domain or in frequency domain. This was added because the time-domain transmission gave some unexpected not-so-correct results, and the fully correct results were only obtained by the frequency-domain transmission.
By default, time-domain transmission is used. To use frequency-domain transmission, you need to specify the OFDM parameters according to the ones used by your transmitter and receiver. If any num_carrier greater than one is used, the frequency domain transmission is used. Otherwise the time domain transmission is used. In terms of computational time, surprisingly the frequency-domain transmission is faster than the other by about 30%.
Note that this class also has the Properties of its base classes. The direct base class is mimo::MIMOChannel ; direct link to its propertylist should be propertylist_MIMOChannel(). The list below usually includes the properties that have been inherited from the base classes; the properties which belong only to this class can be found at the end of this list.

snr

<string>, default "" -- The name of the snr loop variable in this simulation.

channel_refresh

<string>, default "" -- The name of the refresh loop variable in this simulation.

nr_tx

<unsigned>, default "" -- The number of transmit antennas

nr_rx

<unsigned>, default "" -- The number of receive antennas

diagonal

<bool>, default "false" -- If true, then this channel has a diagonal channel matrix i.e. it is not a MIMO channel. However, it is unclear whether the SNR is correct or whether the SNR might be offset by the matrix size. This property is probably only useful for initial testing of mimo algorithms.

5 properties in this class. The above properties have been inherited from the base class mimo::MIMOChannel .

num_path

<unsigned>, default "30" -- Old WSSUS2 parameter for backward compatibility: The minimum number of scattering paths in the WSSUS2 channel model, which might be ignored anyway. In this WSSUS-MIMO model, the *actual* total number of scattering paths is calculated by L_T*L_R*K (see below). If the actual number L_T*L_R*K is smaller than this value, then K is increased until the product is large enough. If the actual number L_T*L_R*K is larger than this property, then it is ignored.

num_tx_scatterers

<unsigned>, default "" -- Important MIMO parameter in WSSUS2 model: Number of distinct transmission angles. In the accompanying research paper, this number is called L_T.

num_rx_scatterers

<unsigned>, default "" -- Important MIMO parameter in WSSUS2 model: Number of distinct receiver angles. In the accompanying research paper, this number is called L_R.

paths_per_scatterers

<unsigned>, default "" -- Important MIMO parameter in WSSUS2 model: Number of paths between two different scatterers. In the accompanying research paper, this number is called K. This number should be chosen so that the product L_T*L_R*K is 30 or greater. If you choose this number smaller, you should consider setting the property path_ampl_random to true.

array_geometry_rx

<enum>, default "linear" -- Geometry of the receiver antenna array

array_geometry_tx

<enum>, default "linear" -- Geometry of the transmitter antenna array

path_ampl_random

<bool>, default "false" -- If true, then the amplitudes of the paths are random according to a Rayleigh distribution. Otherwise they are fixed (unity).

rice_factor_db

<double>, default "-1e6" -- The rice factor of this channel in dB. If unset (minus infinity), then there is no line of sight. The dB property overrides the scalar one.

rice_factor

<double>, default "0.0" -- The rice factor of this channel as a scalar. If unset (zero), then there is no line of sight.

normalization_mode

<enum>, default "standard" -- The normalization mode in this channel: standard, time, or freq. Additionally the channel will be normalized by the number of transmit antennas.

normalization_duration

<unsigned>, default "0" -- Only for normalization mode 'time' or 'frequency': If this is greater than one, then for normalization calculate the norm over several timesteps (= OFDM symbols) instead of the whole duration of the simulation. For a time-variant channel, this will result in some kind of time-variant normalization. Usually this is unused (and for time-invariant channels it doesnt make a difference anyway), but in highly time-variant channels you have to think about your normalization much more carefully.

freq_dist

<double>, default "312500" -- Only for normalization mode 'frequency': Distance of frequence samples when calculating the normalization factor in frequency normalization mode

num_freqs

<unsigned>, default "64" -- Only for normalization mode 'frequency': Number of frequency points/samples when calculating the normalization factor in frequency normalization mode

oversampling

<unsigned>, default "1" -- Only for calculating the correct delta_t: The oversampling rate used by the IDFT (IFFT)

num_carrier

<unsigned>, default "1" -- Only for calculating the correct delta_t: The number of subcarriers where the transfer function is calculated. If this is zero or one, the time-domain transmission will be used instead.

carrier_dist

<double>, default "0.0" -- Only for calculating the correct delta_t: The subcarrier distance on which the transfer function is calculated.

antenna_coupling_ampl

<double>, default "0.0" -- For MIMO antenna coupling: The amplitude of antenna coupling as a scalar (not in dB). If zero, then this is unused.

coupling_phase_random

<bool>, default "false" -- For MIMO antenna coupling: If the antenna_coupling_ampl is greater than zero, then this property determines whether the phases of the coupling coefficients are zero or are random.

18 properties in this class.

Member Data Documentation

unsigned mimo::WSSUSChannel2::num_paths [protected]

Total number of independent propagation paths, as calculated from L_T*L_R*paths_per_scatterer below.

double mimo::WSSUSChannel2::max_delay [protected]

maximal delay time

double mimo::WSSUSChannel2::max_doppler [protected]

Maximum doppler frequency.

unsigned mimo::WSSUSChannel2::L_T [protected]

Number of transmit scatterers.

unsigned mimo::WSSUSChannel2::L_R [protected]

Number of receive scatterers.

unsigned mimo::WSSUSChannel2::paths_per_scatterer [protected]

Number of paths between one transmit scatterer and one receive scatterer (=K)

ScatVect mimo::WSSUSChannel2::scatterers_tx [protected]

Transmit scatterer data.

CMatrix mimo::WSSUSChannel2::steering_tx [protected]

Transmit steering matrix, calculated from the scatterer data.

CMatrix mimo::WSSUSChannel2::doppler_tx [protected]

ScatVect mimo::WSSUSChannel2::scatterers_rx [protected]

Receive scatterer data.

CMatrix mimo::WSSUSChannel2::steering_rx [protected]

Receive steering matrix, calculated from the scatterer data.

CMatrix mimo::WSSUSChannel2::doppler_rx [protected]

PathVect mimo::WSSUSChannel2::h_pathparams [protected]

The path parameters.

CMatrixSeq::storage_type mimo::WSSUSChannel2::h_paths [protected]

The impulse response with the paths between the scatterers, calculated from the path parameters

AntennaArray* mimo::WSSUSChannel2::array_geometry_tx [protected]

Geometry of the tx antenna array.

AntennaArray* mimo::WSSUSChannel2::array_geometry_rx [protected]

Geometry of the rx antenna array.

double mimo::WSSUSChannel2::delta_t [protected]

Sampling time of the sequences to be transmitted.

VectorTimeSignal::storage_type mimo::WSSUSChannel2::prevsym [protected]

previously transmitted samples of one OFDM symbol

bool mimo::WSSUSChannel2::firstSequence [protected]

Is true after initialization or refresh() and is set to false as soon as the first time signal samples are transmitted through this channel. I.e., this is true if and only if there are no previous signal samples stored in WSSUSChannel2::prevsym.

MatrixTimeSignal::storage_type mimo::WSSUSChannel2::imp_resp [mutable, protected]

The matrix-valued impulse response of this channel.

MatrixFreqSignal::storage_type mimo::WSSUSChannel2::cacheTransfer [mutable, protected]

int mimo::WSSUSChannel2::cacheTime [mutable, protected]

Time for which the cached transfer function was valid.

bool mimo::WSSUSChannel2::isTransferCacheValid [mutable, protected]

bool mimo::WSSUSChannel2::timevariant [protected]

Whether this channel is time variant at all.

int mimo::WSSUSChannel2::current_time [protected]

The current time in samples.

Generated on Tue Aug 9 14:44:36 2005 for mimolib by

1.4.1

mimo::WSSUSChannel2 Class Reference

Public Member Functions

Protected Types

Protected Member Functions

Protected Attributes