This class implements an OFDM modulation with the same carrier spacing as WiFi but with somewhat fewer subcarriers, in order to work well with the USRP with 25MHz sample-rate. The matlab functions mod_OFDM1.m and demod_OFDM1 implement basically the same modulation scheme. More...

#include <modem_OFDM1.hpp>

Public Member Functions
	OFDM1 (void)
	Constructor without arguments. Use init to set parameters. See the members for more understanding of the class. The matlab functions mod_OFDM1.m and demod_OFDM1.m implements an more or less identical OFDM.
uint32_t	Nfftr (void)
	Return FFT size.
uint32_t	number_of_modulation_symbols (void)
	Return number of modulation symbols, e.g. 16QAM, in the frame.
uint32_t	waveform_length (void)
	Return number of samples in the time-domain of the complete frame of OFDM symbols.
uint32_t	prefix_length (void)
	Return cyclic prefix length.
ivec	start_of_known_symbol (void)
	Return a vector containing the samples indecies where the known pilot symbols start.
void	init_multi_antenna (uint32_t no_ant, int32_t buffer_size, ivec &interferer_pos)
	Call this function to enable multi-antenna reception using extract_multi_antenna. The multi-antenna reception store signals in internal members. This command create allocates storage for those members.
void	pilot_pattern (cvec &burst, cvec precoder)
	Not part og the API.
void	insert_pilot (cvec &waveform, uint32_t symbol_number, uint32_t offset, cvec precoder)
	Insert a pilot OFDM symbol. Used to insert extra pilot symbols e.g. used for CSI estimation.
void	modulate (cvec &waveform, const cvec &symbols_in, const uint32_t offset, double &rms_power, const cvec &precoder)
	Create the time-domain signal of the modulation i.e. OFDM multiplexing.
void	estimate_channel (cvec waveform, double &noise_variance_normalized, cvec &h, uint32_t start_sample)
	Estimate frequency domain channel.
void	estimate_channel (cvec waveform, double &noise_variance_normalized, cvec &h, uint32_t start_sample, double &noise_variance)
	Estimate frequency domain channel.
void	demodulate (const cvec &waveform, cvec &symbols_out, uint32_t start_sample, const cvec &h, double &rms_signal)
	Perform OFDM single antenna de-multiplexing i.e. extract symbols from time domain signal.
void	demodulate_multi_antenna (const cmat &waveform, vec &soft_bit, uint32_t start_sample, int modulation_order)
	Not part of the API,.
void	extract_multi_antenna (const cmat &waveform, uint32_t start_sample)
	This is a function with side effects. The function makes an MMSE estimate of the subcarrier symbols from the input waveform based on the pilot symbols of the desired and interfering signals. The result is stored in the member matrix x_c where each row correspond to a subcarrier and each column to a payload OFDM symbol.
void	extract_multi_antenna (const cmat &waveform, uint32_t start_sample, cvec &symbols_out)
	This is a function with side effects. The function makes an MMSE estimate of the subcarrier symbols from the input waveform based on the pilot symbols of the desired and interfering signals. The result is stored in the member matrix x_c where each row correspond to a subcarrier and each column to a payload OFDM symbol. The function then equalizes the received signal and puts the result in the vector symbols.
void	synchronize (cvec &waveform, uint32_t &start_pos, double &f_offset)
void	synchronize (cvec &waveform, uint32_t &start_pos)
void	init (bool use_pilot_carriers, bool prepend_training, uint32_t prefix_length, uint32_t Ns, ivec known_pos, ivec re_order)
	This function sets the tunable OFDM parameters.
void	interleave_symbols (cvec &symbol, int index)
	This function performs (in place) interleaving of the subcarriers.
void	de_interleave_symbols (cvec &symbol, int index)
	This function performs (in place) de-interleaving of the subcarriers.
void	pz_init_fft (void)
void	pz_fft (const cvec &in, cvec &out)
void	pz_ifft (const cvec &in, cvec &out)
Public Attributes
ivec	known_symbol_pos
ivec	interferers_known_pos
uint32_t	Ns
complex< double >	pilot_symbol
ivec	ix
ivec	ix_all
ivec	ix_sub
cvec	debug1
cvec	debug2
uint32_t	length_ix
uint32_t	length_ix_all
int	pilot_carrier1_sub
int	pilot_carrier2_sub
int	rightmost_carrier_sub
int	leftmost_carrier_sub
cvec	train
cvec	h
cvec	pulse_shape
int	pulse_shape_delay
bool	do_use_pilot_carriers
bool	do_prepend_training
uint32_t	Np
ivec	d_reorder
double	pilot_power_factor
cmat	he
cmat	hi [10]
cmat	x [100]
cmat	x_c
bool	estimate_SINR
double	SINR
int	noise_estimation_start_ix
int	noise_estimation_stop_ix
cmat	Wfft
cmat	Wifft
imat	symbol_interleave_matrix
imat	symbol_de_interleave_matrix
Static Public Attributes
static const uint32_t	rightmost_carrier = 19
static const uint32_t	leftmost_carrier = 61
static const uint32_t	Nfft = 80
static const uint32_t	pilot_carrier1 = 10
static const uint32_t	pilot_carrier2 = 71
static const uint32_t	Nfft_sync = 65536
static const uint32_t	gap = 3

Detailed Description

This class implements an OFDM modulation with the same carrier spacing as WiFi but with somewhat fewer subcarriers, in order to work well with the USRP with 25MHz sample-rate. The matlab functions mod_OFDM1.m and demod_OFDM1 implement basically the same modulation scheme.

Definition at line 42 of file modem_OFDM1.hpp.

Member Function Documentation

void OFDM1::de_interleave_symbols	(	cvec &	symbol,
		int	index
	)

This function performs (in place) de-interleaving of the subcarriers.

Parameters:

symbol	The symbols of the frame. Uninterleaved on calling and interleaved after return.
index	This parameter can be used change between interleavers. Currently eight interleavers are implemented. Modulo eight is therefore done on index before processing.

Definition at line 821 of file modem_OFDM1.cpp.

void OFDM1::demodulate	(	const cvec &	waveform,
		cvec &	symbols_out,
		uint32_t	start_sample,
		const cvec &	h,
		double &	rms_signal
	)

Perform OFDM single antenna de-multiplexing i.e. extract symbols from time domain signal.

Parameters:

waveform	Input signal.
symbols_out.	Noisy samples of e.g. 16QAM symbols. Length number_of_modulation_symbols().
start_sample.	Where in the waveform to start demodulation.
h.	The channel estimate.
rms_signal.	The RMS received signal strength (unit LSB).

Definition at line 684 of file modem_OFDM1.cpp.

void OFDM1::estimate_channel	(	cvec	waveform,
		double &	noise_variance_normalized,
		cvec &	h,
		uint32_t	start_sample
	)

Estimate frequency domain channel.

Parameters:

waveform	Input signal.
noise_variance_normalized	Estimated noise variance after channel equalization.
h.	Channel estimate.
start_sample	Where in the waveform the known symbol is located.

Definition at line 334 of file modem_OFDM1.cpp.

void OFDM1::estimate_channel	(	cvec	waveform,
		double &	noise_variance_normalized,
		cvec &	h,
		uint32_t	start_sample,
		double &	noise_variance
	)

Estimate frequency domain channel.

Parameters:

waveform	Input signal.
noise_variance_normalized	Estimated noise variance after channel equalization.
h.	Channel estimate.
noise_variance	Noise variance before equalization.
start_sample	Where in the waveform the known symbol is located.

Definition at line 343 of file modem_OFDM1.cpp.

void OFDM1::extract_multi_antenna	(	const cmat &	waveform,
		uint32_t	start_sample
	)

This is a function with side effects. The function makes an MMSE estimate of the subcarrier symbols from the input waveform based on the pilot symbols of the desired and interfering signals. The result is stored in the member matrix x_c where each row correspond to a subcarrier and each column to a payload OFDM symbol.

Parameters:

waveform	A matrix with the received signal samples. Each row correspond to a receive antennas.
start_sample	First sample where to start demultiplexing.

Definition at line 593 of file modem_OFDM1.cpp.

void OFDM1::init	(	bool	use_pilot_carriers,
		bool	prepend_training,
		uint32_t	prefix_length,
		uint32_t	Ns,
		ivec	known_pos,
		ivec	re_order
	)

This function sets the tunable OFDM parameters.

Parameters:

use_pilot_carriers	If true, then two out ot 38 subcarriers use known symbols to aid receiver processing e.g. compensation of phase-noise and frequency offset. Typically not needed.
prepend_training	If true a training sequence (or rather a synchronization sequence) is insterted before the OFDM symbols. Typically not needed.
prefix_length	Length of cyclic prefix is samples. The length of the OFDM symbols is 80 samples without cyclic prefix.
Ns.	Number of symbols per frame including pilot symbols.
known_pos.	Vector with the positions of known symbols.
re_order.	The position index of the k:th symbol (k=0,...,Ns-1) is re_order(k).

Definition at line 54 of file modem_OFDM1.cpp.

void OFDM1::init_multi_antenna	(	uint32_t	no_ant,
		int32_t	buffer_size,
		ivec &	interferer_pos
	)

Call this function to enable multi-antenna reception using extract_multi_antenna. The multi-antenna reception store signals in internal members. This command create allocates storage for those members.

Parameters:

no_ant	Number of receiver antennas to be used.
buffer_size	Time domain length (in samples) of the received antenna data.
interferer_pos	The symbol positions in the frame where the interferers are transmitting their pilot symbols.

Definition at line 398 of file modem_OFDM1.cpp.

void OFDM1::insert_pilot	(	cvec &	waveform,
		uint32_t	symbol_number,
		uint32_t	offset,
		cvec	precoder
	)

Insert a pilot OFDM symbol. Used to insert extra pilot symbols e.g. used for CSI estimation.

Parameters:

waveform	Time domain samples.
symbol_number	Position of the symbol in the burst.
offset	Number of samples to offset the insertion.
precoder	A vector of complex values to multiply the pilot subcarriers with. Use for linear precoding (aka beamforming).

Definition at line 320 of file modem_OFDM1.cpp.

void OFDM1::interleave_symbols	(	cvec &	symbol,
		int	index
	)

This function performs (in place) interleaving of the subcarriers.

Parameters:

symbol	The symbols of the frame. Uninterleaved on calling and interleaved after return.
index	This parameter can be used change between interleavers. Currently eight interleavers are implemented. Modulo eight is therefore done on index before processing.

Definition at line 806 of file modem_OFDM1.cpp.

void OFDM1::modulate	(	cvec &	waveform,
		const cvec &	symbols_in,
		const uint32_t	offset,
		double &	rms_power,
		const cvec &	precoder
	)

Create the time-domain signal of the modulation i.e. OFDM multiplexing.

Parameters:

waveform	The time domain samples.
symbols_in	The complex symbols to be transmitted. The length of which is given by number_of_modulation_symbols().
offset	Number of samples offset into the burst.
rms_power	Returns the rms_power of the transmitted time-domain waveform. If rms_pwer=-10 on calling, the rms_power is not calculated which reduces the computational load.
precoder	A vector of complex values to multiply the pilot subcarriers with. Use for linear precoding (aka beamforming).

Definition at line 238 of file modem_OFDM1.cpp.

void OFDM1::pz_fft	(	const cvec &	in,
		cvec &	out
	)		`[inline]`

This function is not part of the API

Definition at line 292 of file modem_OFDM1.hpp.

void OFDM1::pz_ifft	(	const cvec &	in,
		cvec &	out
	)		`[inline]`

This function is not part of the API

Definition at line 295 of file modem_OFDM1.hpp.

void OFDM1::pz_init_fft ( void ) [inline]

This function is not part of the API

Definition at line 269 of file modem_OFDM1.hpp.

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

modem/modem_OFDM1.hpp
modem/modem_OFDM1.cpp

Public Member Functions

Public Attributes

Static Public Attributes

Detailed Description

Member Function Documentation