Tapped Delay Line (TDL) channel model. More...

#include <itpp/comm/channel.h>

Public Member Functions
	TDL_Channel (const vec &avg_power_dB="0", const ivec &delay_prof="0")
	Default constructor.

	TDL_Channel (const Channel_Specification &channel_spec, double sampling_time)
	Constructor with defined Channel_Specification. Delay profile will be discretized with sampling_time in seconds.

virtual	~TDL_Channel ()
	Destructor.

void	set_channel_profile (const vec &avg_power_dB, const ivec &delay_prof)
	Set both average power profile in dB and power delay profile in samples.

void	set_channel_profile_uniform (int no_taps)
	Set channel profile to uniform with no_taps taps.

void	set_channel_profile_exponential (int no_taps)
	Set channel profile to exponential with no_taps taps.

void	set_channel_profile (const Channel_Specification &channel_spec, double sampling_time)
	Set channel profile using Channel_Specification. Delay profile will be discretized with sampling_time in seconds.

void	set_correlated_method (CORRELATED_METHOD method)
	Set the fading generation method to method.

void	set_fading_type (FADING_TYPE fading_type)
	Set fading type to one of Independent, Static or Correlated.

void	set_norm_doppler (double norm_doppler)
	Set normalized Doppler rate. A Correlated fading type will be used.

void	set_LOS (const vec &relative_power, const vec &relative_doppler="")
	Set LOS parameters for each tap. LOS Doppler will be set to 0.7 by default.

void	set_LOS_power (const vec &relative_power)
	Set LOS power for each tap. LOS Doppler will be set to 0.7 by default.

void	set_LOS_doppler (const vec &relative_doppler)
	Set LOS doppler for each tap. A Correlated fading type will be used.

void	set_doppler_spectrum (const DOPPLER_SPECTRUM *tap_spectrum)
	Set doppler spectrum for each tap in the channel profile. Rice_MEDS method will be used.

void	set_doppler_spectrum (int tap_number, DOPPLER_SPECTRUM tap_spectrum)
	Set doppler spectrum of tap tap_number. Rice_MEDS method will be used.

void	set_no_frequencies (int no_freq)
	Set number of sine frequencies. Rice_MEDS method will be used.

void	set_time_offset (int offset)
	Set fading generators' time offset in samples. A Correlated fading type will be used.

void	shift_time_offset (int no_samples)
	Shift fading generators' time offset. A Correlated fading type will be used.

void	set_filter_length (int filter_length)
	Set fading generator filter length. FIR method will be used.

int	taps () const
	Return the number of channel taps.

void	get_channel_profile (vec &avg_power_dB, ivec &delay_prof) const
	Get both average power profile in dB and power delay profile in samples.

vec	get_avg_power_dB () const
	Return power profile in dB.

ivec	get_delay_prof () const
	Return delay profile in samples.

CORRELATED_METHOD	get_correlated_method () const
	Return fading generation method.

FADING_TYPE	get_fading_type () const
	Return fading type.

double	get_norm_doppler () const
	Return normalized doppler rate.

vec	get_LOS_power () const
	Get relative power (Rice factor) for each tap.

vec	get_LOS_doppler () const
	Get relative Doppler (to the maximum Doppler) for each tap.

double	get_LOS_power (int tap_number) const
	Get relative power (Rice factor) for tap tap_number.

double	get_LOS_doppler (int tap_number) const
	Get relative Doppler (to the maximum Doppler) for tap tap_number.

int	get_no_frequencies () const
	Get the minimum number of frequencies used in Rice MEDS fading generator.

double	get_time_offset () const
	Get fading generators' time ofset.

double	calc_mean_excess_delay () const
	Calculate mean excess delay in samples.

double	calc_rms_delay_spread () const
	Calculate RMS delay spread in samples.

void	init ()
	Initialize all fading generators. Automatically invoked in generate() or filter() functions.

void	generate (int no_samples, Array< cvec > &channel_coeff)
	Generate no_samples values of the channel.

void	generate (int no_samples, cmat &channel_coeff)
	Generate no_samples values of the channel. Returns the matrix with one tap per column.

void	filter_known_channel (const cvec &input, cvec &output, const Array< cvec > &channel_coeff)
	Filter the input with the known channel values channel_coeff (e.g. from the generate function)

void	filter_known_channel (const cvec &input, cvec &output, const cmat &channel_coeff)
	Filter the input with the known channel values channel_coeff (e.g. from the generate function)

void	filter (const cvec &input, cvec &output, Array< cvec > &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

void	filter (const cvec &input, cvec &output, cmat &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

cvec	filter (const cvec &input, Array< cvec > &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

cvec	filter (const cvec &input, cmat &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

void	filter (const cvec &input, cvec &output)
	Generate channel coefficients and filter the input. Only return the output.

cvec	filter (const cvec &input)
	Generate channel coefficients and filter the input. Only return output.

void	operator() (const cvec &input, cvec &output, Array< cvec > &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

void	operator() (const cvec &input, cvec &output, cmat &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

cvec	operator() (const cvec &input, Array< cvec > &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

cvec	operator() (const cvec &input, cmat &channel_coeff)
	Generate channel coefficients and filter the input. Return output and channel coefficients.

cvec	operator() (const cvec &input)
	Generate channel coefficients and filter the input. Only return output.

void	calc_impulse_response (const Array< cvec > &channel_coeff, Array< cvec > &impulse_response)
	Calculate impulse-response on the supplied channel coefficients (produced by the generate() function)

void	calc_frequency_response (const Array< cvec > &channel_coeff, Array< cvec > &frequency_response, const int fft_size)
	Calculate frequency-response on the supplied channel coefficients (produced by the generate() function)

void	calc_frequency_response (const cmat &channel_coeff, cmat &frequency_response, const int fft_size)
	Calculate frequency-response on the supplied channel coefficients (produced by the generate() function)

double	get_sampling_time () const
	Return channel sampling time (used for discretization)

Protected Member Functions
void	discretize (const vec &delay_profile)
	Discretize the delay profile with discrete_Ts (Ts). All taps within ((i-0.5)Ts,(i+0.5)Ts] belong to the ith discrete tap.

Protected Attributes
bool	init_flag
	Channel ready to produce data.

vec	a_prof
	Average amplitude of each tap.

ivec	d_prof
	Delay in samples for each tap.

vec	los_power
	Relative power for each Rice component.

vec	los_dopp
	Relative LOS Doppler for each Rice component.

int	N_taps
	Number of taps.

double	n_dopp
	Normalized Doppler of the correlated fading.

FADING_TYPE	fading_type
	Fading type: Independent (default), Static or Correlated.

CORRELATED_METHOD	method
	Correlated fading generation method: Rice_MEDS (default), IFFT or FIR.

Array< DOPPLER_SPECTRUM >	tap_doppler_spectrum
	Doppler spectrum for each tap.

Array< Fading_Generator * >	fading_gen
	Fading generators for each tap.

int	filter_length
	Filter length of FIR fading generator.

int	nrof_freq
	Number of sine frequencies in the Rice MEDS fading generator.

double	discrete_Ts
	Sampling time of discretization.

Detailed Description

Tapped Delay Line (TDL) channel model.

Author: Tony Ottosson, Adam Piatyszek and Zbigniew Dlugaszewski

A time invariant (or at least wide-sense stationary) channel have an impulse response that can be modeled as:

$h(t) = \sum_{k=0}^{N_\mathrm{taps}-1} a_k \exp (-j \theta_k ) \delta(t-\tau_k),$

where $N_{taps}$ is the number of channel taps, $ a_k $ is the average amplitude at delay $\tau_k$ , and $\theta_k$ is the channel phase of the $k^{th}$ channel tap. The average power profile, and delay profile are defined as:

$\mathbf{a} = [a_0, a_1, \ldots, a_{N_\mathrm{taps}-1}]$

and

$\mathbf{\tau} = [\tau_0, \tau_1, \ldots, \tau_{N_\mathrm{taps}-1}],$

respectively. We assume without loss of generality that $\tau_0 = 0$ and $\tau_0 < \tau_1 < \ldots < \tau_{N_\mathrm{taps}-1}$ .

To initialize the channel profile the following parameters should be defined:

avg_power_dB Average power profile $\mathbf{a}$ , given in dB
delay_profile Delay profile $\mathbf{\tau}$ , given in samples. The delay profile should be sorted (increasing delay) and the first delay has to be 0.

In the case of correlated channel, the correlation in time is decided by the normalized Doppler frequency and Doppler spectrum. The normalized Doppler frequency is calculated as $f_\mathrm{max} T_s$ , where $f_\mathrm{max}$ is the maximum Doppler frequency and $ T_s $ is the sample duration.

Two main types of generation methods exist: the filter method and Rice method. In the filter method the correlated fading process is generated with a filtering of the complex Gaussian process to achieve a given Doppler spectrum (Jakes by default). Currently there are two filter implementations:

FIR - Finite Impulse Response (FIR) filter. Rather slow and inaccurate. Use with care.
IFFT - Blockwise filtering in the frequency-domain. Consecutive blocks have independent fading. Very efficient method for large blocks.

The preferred method for generating the correlated fading process is the Rice method that approximate the fading process as a sum of sinusoids. Currently there is only one implementation, the Rice Method of Exact Doppler Spread (Rice_MEDS), which is also the default choice.

To summarize, the currently supported correlated fading generation methods are:

FIR - filter FIR method
IFFT - filter IFFT method
Rice_MEDS - sum of sine waves MEDS method

Beside the above described correlated methods, two additional fading generators exists: the Independent_Fading_Generator and Static_Fading_Generator ones. Their names are self-explanatory. The only optional parameter of these two generators is a relative_power of the LOS component.

Example: Simulation of WCDMA

#include <itpp/itcomm.h>
using namespace itpp;
int main() {
  // set sampling time at a half of chip rate (0.5 / 3.84e6)
  double Ts = 130.2e-9;
  // select the COST259 Rural Area model
  Channel_Specification channel_spec(COST259_RAx);
  // initialize with the predefined channel profile
  TDL_Channel channel(channel_spec, Ts);
  // set the normalized Doppler; fading type will be set to Correlated
  // and Rice_MEDS method will be used (default settings)
  channel.set_norm_doppler(0.01);
  cvec transmitted_signal;
  // -----------------------------------------------
  // Your code here generates the transmitted signal
  // -----------------------------------------------
  // Channel coefficients are returned in the 'coeff' array of complex values
  Array<cvec> coeff;
  cvec received_signal = channel(transmitted_signal, coeff);
}

References:

[Pat02] Matthias Patzold, Mobile fading channels, Wiley, 2002.
[Stu01] Gordon L. Stuber, Principles of mobile communication, 2nd. ed., Kluwer, 2001.
[Rap96] Theodore S. Rappaport, Wireless communications: principles and practise, Prentice Hall, 1996.

Definition at line 857 of file channel.h.

Member Function Documentation

void itpp::TDL_Channel::discretize ( const vec & delay_profile )

protected

Discretize the delay profile with discrete_Ts (Ts). All taps within ((i-0.5)Ts,(i+0.5)Ts] belong to the ith discrete tap.

Parameters

delay_profile Delay profile in seconds.

Definition at line 1447 of file channel.cpp.

References a_prof, d_prof, discrete_Ts, itpp::elem_div(), it_assert, it_warning, los_dopp, los_power, N_taps, itpp::round_i(), itpp::Array< T >::set_size(), itpp::Array< T >::size(), itpp::sqr(), itpp::sqrt(), and tap_doppler_spectrum.

Referenced by set_channel_profile().

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

itpp/comm/channel.h
itpp/comm/channel.cpp

Public Member Functions

Protected Member Functions

Protected Attributes

Detailed Description

Member Function Documentation