Classes | |
class | itpp::Fading_Generator |
Fading generator class. More... | |
class | itpp::Rice_Fading_Generator |
Rice type Fading generator class. More... | |
class | itpp::FIR_Fading_Generator |
FIR type Fading generator class. More... | |
class | itpp::IFFT_Fading_Generator |
IFFT type Fading generator class. More... | |
class | itpp::Channel_Specification |
General specification of a time-domain multipath channel. More... | |
class | itpp::TDL_Channel |
Tapped Delay Line (TDL) channel model. More... | |
class | itpp::BSC |
A Binary Symetric Channel with crossover probability p. More... | |
class | itpp::AWGN_Channel |
Ordinary AWGN Channel for cvec or vec inputs and outputs. More... | |
Enumerations | |
enum | itpp::DOPPLER_SPECTRUM { Jakes = 0, J = 0, Classic = 0, C = 0, GaussI = 1, GI = 1, G1 = 1, GaussII = 2, GII = 2, G2 = 2, Rice = 3, R = 3 } |
Predefined doppler spectra. More... | |
enum | itpp::RICE_METHOD { MEDS } |
Methods calculation of parameters using the Rice fading generation method. More... | |
enum | itpp::FADING_GENERATION_METHOD { IFFT, FIR, Rice_MEDS } |
Fading generation methods. More... | |
enum | itpp::CHANNEL_PROFILE { ITU_Vehicular_A, ITU_Vehicular_B, ITU_Pedestrian_A, ITU_Pedestrian_B, COST207_RA, COST207_RA6, COST207_TU, COST207_TU6alt, COST207_TU12, COST207_TU12alt, COST207_BU, COST207_BU6alt, COST207_BU12, COST207_BU12alt, COST207_HT, COST207_HT6alt, COST207_HT12, COST207_HT12alt, COST259_TUx, COST259_RAx, COST259_HTx } |
Predefined channel profiles. Includes settings for doppler spectrum. More... | |
Functions | |
vec | itpp::jake_filter (double NormFDopp, int order) |
Jakes spectrum filter. |
Multipath fading is the process where the received signal is a sum of many reflections each with different propagation time, phase and attenuation. The sum signal will vary in time if the receiver (or transmitter) moves or if some of the reflectors move. We usually refer to this process as a fading process and try to model it as a stochastic process. The most common model is the Rayleigh fading model where the process is modeled as a sum of infinitely many (in practise it is enough with only a few) received reflections from all angles (uniformly) around the receiver. Mathematically we write the receieved signal, as
where is the transmitted signal and
is the complex channel coefficient (or fading process). If this process is modeled as a Rayleigh fading process then
is a complex Gaussian process and the envelope
is Rayleigh distributed.
where is the maximum doppler frequency given by
Here is the speed of light and
is the carrier frequency. Often the maximum doppler frequency is given as the normalized doppler
, where
is the sample duration (often the symbol time) of the simulated system. Instead of specifing the correlation fuction
we can specify the doppler spectrum (the fourier transform of
).
where is the number of channel taps,
is the average amplitude at delay
, and
is the channel phase of the
th channel tap. The average power profile, and the delay profiles are defined as:
and
respectively. We assume without loss of generality that and
. Now the received signal is simpy a linear filtering (or convolution of the transmitted signal) where,
is impulse response of the filter.
In practise, when simulating a communication link, the impulse response is sampled with a sample period
that is related to the symbol rate of the system of investigation (often 2-8 times higher). Hence, the impulse respone of the channel can now be modeled as a time-discrete filter or tapped-delay line (TDL) where the delays are given as
, and
are positive integers.
The LOS component can be expressed as:
where ,
, and
are the amplitude, doppler frequency and phase of the LOS component, respectively. Instead of stating the amplitude itself the ratio of the LOS power and the fading process power (or relative power), often called the Rice factor, is often stated. The doppler frequency is limited by the maximum doppler frequency
and hence typically the doppler of the LOS is expressed relative to its maximum (common is
). The phase is usually assumed to be random and can without loss of generality be set to 0 (does not affect the statistics of the process).
[Stuber] Gordon L. Stuber, Principles of mobile communication, 2nd. ed., Kluwer, 2001.
[Rappaport] Theodore S. Rappaport, Wireless communications: principles and practise, Prentice Hall, 1996.
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Predefined doppler spectra.
Definition at line 172 of file channel.h. Referenced by itpp::Fading_Generator::get_doppler_spectrum(). |
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Methods calculation of parameters using the Rice fading generation method.
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Fading generation methods.
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Predefined channel profiles. Includes settings for doppler spectrum.
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Jakes spectrum filter. Function that generates the taps in the Jake-filter. order is the number of taps in the filter. NormFdopp is the normalized doppler frequency, i.e. NormFDopp = Fd * Ts, where Fd is the acctual Doppler frequency and Ts is the sampling interval. Returns a vector containing the filter taps of the Jake-filter. Definition at line 44 of file channel.cpp. References itpp::besselj(), itpp::floor(), itpp::hamming(), itpp::norm(), itpp::reverse(), and itpp::sqrt(). |
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