BERT_v1 Class Reference

Contains the implementation of a BER counter. More...

Inherits unit.

Public Member Functions
function	BERT_v1 (in param)
	Class constructor. More...
function	traverse (in obj, in sig, in refSig)
	Main function. More...
function	bert (in obj, in srx)
	Error counter. More...
function	obtainPRBS (in obj, in sig)
	Locates and returns the repeating sequence. More...
function	ProcessBER (in obj)
	Error post-processor. More...
function	plot (in obj, in srx, in ErrorMap, in i)
	Main plotting function. More...
function	initPlot (in obj, in srx)
	Initialize plot. More...
function	plotErrors (in obj, in ErrorMap, in i)
	Plot errorgram. More...
function	plotHistogram (in obj, in srx, in jj)
	Histogram plotting function. More...
function	plotResults (in obj, in pos, in res)
	Result plotting function. More...
function	printResults (in obj)
	Result printing function. More...
Public Member Functions inherited from unit
virtual	traverse (in obj, in varargin)
	Main function call.
function	traverseNode (in obj)
	Set unique ID when creating a unit. More...
function	connectOutput (in obj, in uobj, in unitOutput, in nextUnitInput)
	Specify where signal should go next. More...
function	connectOutputs (in obj, in units, in destInputs)
	Specify where signal should go next. More...
function	writeInputBuffer (in obj, in sig, in inputId)
	write input buffer
function	horzcat (in varargin)
	horizontal concatenation
function	vertcat (in varargin)
	vertical concatenation
function	setparams (in obj, in params, in REQUIRED_PARAMS, in QUIET_PARAMS)
	set parameters More...
function	view (in obj)
	Show interactive GUI through unit_view-class.

Static Public Member Functions
static function	getQ (in M, in srx, in sdemod, in c)
	Calculates PAM quality estimates. More...
static function	getEVM (in srx, in c)
	Calculates EVM quality estimates. More...
static function	BERfromQAMEVM (in EVM, in M)
	Calculates BER from EVM. More...
static function	preEstimatePhase (in srx, in M)
	Quick and dirty phase offset estimate. More...
static function	trimPRBS (in in)
	Gets PRBS from signal. More...
static function	rx (in srx, in M, in Coding)
	K-means based demodulation. More...
static function	skipMargin (in margin, in in)
	Skips symbols at beginning and/or end. More...

Public Attributes
Property	nInputs
Property	nOutputs
Property	M
	Constellation order.
Property	ConstType
	Constellation type {'QAM' | 'ASK' | ... }.
Property	Constellation
	Full Constellation.
Property	TxData
	Transmitted data.
Property	Coding
	Coding gray or binary {'gray' | 'bin'}.
Property	BlockLength
	Block length for error counting.
Property	CounterMethod
	Which counter to use {'generic'}.
Property	DecisionType
	Decision type {'hard' | 'soft'}.
Property	EnableMetrics
	Calculate EVM, Q, etc. {true | false}.
Property	EnableCounter
	Calculate BER, SER, errorgram etc.
Property	PostProcessMethod
	How to identify bad blocks {'none' | 'threshold' | 'probability'}.
Property	FastMode
	Disables Counter and plots only 10000 symbols.
Property	Only
	Only calculate the signal columuns specified in this vector.
Property	Cols
	(internal) Vector containing what columns to demodulate
Public Attributes inherited from unit
Property	inputBuffer
	Buffer for storing inputs as we traverse the graph.
Property	nextNodes
	Children nodes.
Property	destInputs
	Destination inputs in children.
Property	results
	For storing results.
Property	label
Property	draw
	enable/disable plotting
Property	nInputs
	Number of signals traverse expects.
Property	nOutputs
	Number of outputs traverse expects.

Detailed Description

Contains the implementation of a BER counter.

Bit error rate tester. It outputs estimated and computed quality of your signal in terms of Q factor, EVM, Pb, Ps, estimated number of bit errors and symbol errors, as well as the computer BER and SER. If PRBS pattern isn't passed as a parameter, the unit self-sets the number of inputs to 2, so that the 2nd input is the PRBS coming out the pattern generator.

Program Structure

The BERT executes the following functions in the followint order (from BERT_v1::traverse):

1. Count errors and map their locations, using BERT_v1::bert
2. Calculate constellation quality metrics, from BERT_v1::bert, either BERT_v1::getQ or BERT_v1::getEVM is called (depending on constellation type), and the expected BER is calculated either in BERT_v1::bert (for ASK) or BERT_v1::BERfromQAMEVM (for QAM)
3. Choose which blocks to include/exclude in total BER, using BERT_v1::ProcessBER
4. Plot all results

If speed is a concern, the second and fourth steps can be disabled using object proprties EnableMetrics and draw, respectively. Also, FastMode operation allows for only caluclate metrics and plots up to 10000 symbols in the constellation.

Output Structure

The class results structure contains all calculated results. It has two levels of hierarchy:

1. obj.results.<property> describes a property of the entire signal
2. obj.results.Col<N>.<property> describes a property the signal in column N

obj.results will always contain fields 'ber', 'ser', 'totalbits', and 'totalsymbs' (bit error rate, symbol error rate, total bits counted, and total symbols counted). obj.results.Col<N> is a more flexible structure type, whose fields may vary depending on the counting method, post-processing method, modulation format, etc.

If plotting (draw) is enabled, these will be both drawn in a figure and entered into the log. Otherwise, the user is responsible for extracting the information of interest.

See also

error_counter_v7c.m

constref.m

Author

Miguel Iglesias Olmedo

6.2015 Molly Piels

Definition at line 58 of file BERT_v1.m.

Constructor & Destructor Documentation

function BERT_v1::BERT_v1

(

in

param

)

Class constructor.

Class constructor. Required parameters are the constellation order (param.M) and type (param.ConstType, default QAM). See the utils folder for correct syntax for constellation specification.

Additional signal description parameters:

• param.TxData
  Transmitted data. This should be a single cycle of the full transmitted binary PRBS sequence. It can be either logical or double with 1's and 0's.
• param.Coding
  Describes how the binary data is mapped to symbols. The options are with gray coding and binary (delay and add) coding.

Computation-related parameters:

• param.CounterMethod
  Specify the counter to use. This block is meant to hold a number of counters. See BERT_v1::bert for instructions on how to format a counter to incorporate into the block.
• param.BlockLength
  Most counters segment the data into blocks of this length. The post-processing algorithms require segmented data, so it is important to specify this even if the counter used does not require it.
• param.DecisionType
  Many (but not all!) counters allow the user to choose between hard and soft decision. For hard decision, the locations of constellation points are set to be the ideal locations for that constellation. For soft decision, they are chosen by clustering the data using kmeans.
• param.EnableMetrics
  Enable calculating Q, EVM, and associated theoretical number of symbol and bit errors. Should be enabled generally, but runtime improves if it is disabled, which can be useful for parameter scans.
• param.PostProcessMethod
  After counting all errors in the entire sequence, only some are considered when calculting the final BER and SER. This option allows the user to select this criteria. The options are 'probability', 'threshold', and default. The default option is to count all bits received. If 'probability' is selected, the BER is calculated for the whole sequence, and then blocks of symbols are included/excluded based on whether or not the probability of that particular number of errors given this average BER is above a certain threshold. This probability is calculated assuming a binomial distribution. If 'threshold' is selected, all blocks with BER above a certain threshold are rejected. All the associated thresholds are passed to the constructor in the param.PostProcessMethod field, separated by the name of the method by a space. For example:

  param.PostProcessMethod = 'threshold 0.1' 

  will result in all blocks with BER>0.1 being rejected.
• param.FastMode
  - param.draw
  Enable or disable plotting (true results in the plot being generated).

Example:

param.M=4;
param.ConstType='ASK'
param.TxData=gen_prbs(15);
param.Coding = 'bin';
param.DecisionType = 'hard';
param.PostProcessMethod = 'probability 0.999';
bert = BERT_v1(param);

This will create a counter for 4PAM using hard-decision and assuming a delay-and-add mapping of bits to symbols. Only blocks with block-wise BERs with a probability of 0.999 or higher will be considered when the BER for the whole sequence is calculated. The block length will be 2048 symbols, because this is the default. Metrics will be calculated, and a plot will be generated, because this is also default behavior.

Parameters

param.M	Constellation order
param.ConstType	Constellation type {'QAM' | 'ASK' | ...}
param.TxData	Transmitted data (binary sequence)
param.Coding	Coding gray or binary {'gray' | 'bin'}
param.CounterMethod	Counting method {'generic'}
param.BlockLength	How many symbols to consider at once (any integer)
param.DecisionType	Hard vs. soft decision {'hard' | 'soft'}
param.EnableMetrics	Enable calculating Q, EVM, etc. {true | false}
param.EnableCounter	Enable calculating BER, SER, errorgram etc.
param.PostProcessMethod	How to choose what blocks to count {'none' | 'threshold' | 'probability'}
param.draw	Turn plotting on/off {true | false}

Return values

obj	Instance of the BERT_v1 class

Member Function Documentation

static function BERT_v1::BERfromQAMEVM ( in  EVM, in  M  )

static

Calculates BER from EVM.

Calculates BER from EVM, using the formula from [1]

Warning

There is a misprint in [1] Eq. 4. A √2 factor must be removed, as pointed out by [2].

References

[1] Schmogrow et al., "Error Vector Magnitude as a Performance Measure for Advanced Modulation Formats," Photononics Technology Letters, Vol. 24 No. 1, January 2012.

[2] Schmogrow et al., "512 QAM Nyquist sinc-pulse transmission at 54 Gbit/s in an optical bandwidth of 3 GHz." Optics Express Vol. 20, No. 6, 12 March 2012.

Parameters

EVM	error vector magnitude
M	constellation order (M-QAM)

Return values

BER	estimated BER

Author

Gerson Rodriguez de los Santos López

Date

20/11/2012

Author

Miguel Iglesias Olmedo, where EVM is normalized with resect to the average power, instead of the peak power, removing the need of the k factor.

Date

29/11/2014

function BERT_v1::bert	(	in	obj,
		in	srx
	)

Error counter.

Error counter. This part contains the main counting routines and calculates EVM, Q, etc.

In order to be compatible with the rest of this unit, a counter must output the following parameters (some of these are redundant and could be calculated within the switch case):

1. BER per block (array)
2. SER per block (array)
3. Number of bit errors
4. Number of symbol errors
5. Number of bits counted
6. Number of symbols counted
7. Symbol error locations, or both mapped and received symbol sequences

This last one is optional, but obj.EnableCalcMetrics should be disabled if error locations are not returned by the counter. The remaining requirements are each mapped to a field of the output results structure (res). The results structure is quite flexible, and it is OK for a counter to return other values in it as well, but these will not be used elsewhere. Results from this function are stored in obj.results.ColN, where N is an integer corresponding to the signal column.

A compatible counter also must operate on an input signal that has been normalized to unity mean power and has to include a decision mechanism. The object's built-in receiver (BERT_v1::rx) can be used to provide decisions.

Parameters

sig	input signal
refSig	reference PRBS

Return values

res.ber_block	BER per block
res.ser_block	SER per block
res.err_bits	total bit errors
res.err_symb	total symbol errors
res.totalbits	total bits counted
res.totalsymb	total symbols counted
res.Q	Q factor
res.EVM	Error vector magnitude (for QAM)
res.Ps	Symbol error probability (for ASK)
res.Pb	Bit error probability (for ASK)
res.est_bit_errors	Estimated bit errors from Q, EVM, etc.
res.c	cluster centers
res.boundaries	decision boundaries (for ASK)
res.sig	per-level standard deviations (for ASK)
ErrorMap	logical array with 1's representing errors

static function BERT_v1::getEVM ( in  srx, in  c  )

static

Calculates EVM quality estimates.

Calculates EVM quality estimates

Parameters

srx	received symbols
c	centroids

Return values

evm	error vector magnitude

static function BERT_v1::getQ ( in  M, in  srx, in  sdemod, in  c  )

static

Calculates PAM quality estimates.

Calculates PAM quality estimates

Parameters

M	Constellation order (M-PAM)
srx	received symbols
sdemod	demodulated symbols
c	centroids

Return values

Q	Q-factor
boundary	decision boundaries
sig	per level standard deviations

function BERT_v1::initPlot	(	in	obj,
		in	srx
	)

Initialize plot.

Generate plot figure and determine which quantities to plot

Parameters

srx	received data

function BERT_v1::obtainPRBS	(	in	obj,
		in	sig
	)

Locates and returns the repeating sequence.

This can be used to find the PRBS in a sequence

Parameters

sig	input signal (any)

Return values

prbs	extracted PRBS (logical)

function BERT_v1::plot	(	in	obj,
		in	srx,
		in	ErrorMap,
		in	i
	)

Main plotting function.

Main plotting function

Parameters

srx	received data
ErrorMap	logical array showing error locations

function BERT_v1::plotErrors	(	in	obj,
		in	ErrorMap,
		in	i
	)

Plot errorgram.

Plot error locations

Parameters

ErrorMap	error locations
i	Column number

function BERT_v1::plotHistogram	(	in	obj,
		in	srx,
		in	jj
	)

Histogram plotting function.

Histogram plotting function for PAM/ASK signals

Parameters

srx	received data
g	received data
c	received data

function BERT_v1::plotResults	(	in	obj,
		in	pos,
		in	res
	)

Result plotting function.

Prints results into table in figure

Parameters

pos	position
res	results to print

static function BERT_v1::preEstimatePhase ( in  srx, in  M  )

static

Quick and dirty phase offset estimate.

Quick and dirty phase offset estimate

Parameters

srx	input data
M	constellation order (M-QAM)

Return values

phi	estimated phase offset

function BERT_v1::printResults

(

in

obj

)

Result printing function.

Prints results into log (using robolog - this could end up either in the command window or a text file).

See also

robolog.m

Parameters

res	results to print

function BERT_v1::ProcessBER

(

in

obj

)

Error post-processor.

This assesses which blocks or bits to consider when calculating the BER for the whole signal. BER and SER are calculated for the whole signal and for each column individually. Bit errors per block and block size are left unchanged.

For the processing methods that include thresholds, the correct constructor syntax is

param.PostProcessMethod = '<type> <value>'

For 'threshold' type, blocks with BER > value are rejected. For 'probability' type, blocks with probability < value are rejected. The probability is calculated using the average BER for the whole sequence, or 100 errors for the whole sequence, whichever is greater.

Return values

obj.results.ber	BER for the whole signal
obj.results.ser	SER for the whole signal
obj.results.ColN.ber	BER for column N
obj.results.ColN.ser	SER for column N
obj.results.ColN.badblocks	map of rejected block locations

static function BERT_v1::rx ( in  srx, in  M, in  Coding  )

static

K-means based demodulation.

K-means based demodulation

Parameters

srx	input data
M	constellation order (M-QAM)
Coding	coding type {'bin', 'gray'}

Return values

out	received symbols
c	cluster centroids

static function BERT_v1::skipMargin ( in  margin, in  in  )

static

Skips symbols at beginning and/or end.

Skips symbols at beginning and/or end of sequence

Parameters

margin	how much of sequence to skip
in	input data

Return values

symbols

estimated symbol sequence

function BERT_v1::traverse	(	in	obj,
		in	sig,
		in	refSig
	)

Main function.

Main function. Performs basic signal conditioning, calls counter, post-processes, plots, then prints. The BER, SER, and any other requested methods are saved in the object's results property.

Parameters

sig	input signal
refSig	reference PRBS

static function BERT_v1::trimPRBS ( in  in )

static

Gets PRBS from signal.

Gets a signal and outputs a clean PRBS for comparison

Parameters

in	input data

Return values

out	estimated PRBS

---

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

• library/rx/DSP/BERT_v1.m