Version:

Last Modified: February 7, 2018

Calculates the average bit error rate (BER) against a Fibonacci PN sequence. The sequence must be the same as the PN sequence generated by MT Generate Bits (Fibonacci, PN Order) with a matching PN order.

On the first call of this node, or whenever **reset?** is TRUE, the node steps through each set of *N* + 1 bits in the input sequence to generate a seed for the PN bit sequence. Subsequent input bits are compared to this PN bit sequence. When the BER on the subsequent input bits is below the specified threshold with the specified confidence, the node begins reporting the BER. BER calculation begins on the bit following the set of *N* + 1 bits in which the trigger is found. All subsequent iterations of the node use a continuation of the same PN sequence until **reset?** is set to TRUE.

The bit sequence over which BER is calculated. This bit stream must include only data bits of the PN sequence.

The order of the transmitted PN bit sequence. This parameter must match the PN sequence order of the bits transmitted to the device under test. Valid values are 5 to 31, inclusive.

**Default: **9

The BER threshold that must not be exceeded for the **trigger found?** decision. This value determines when the BER measurement begins; bits before this value and seed bits are not included in the BER measurement. Valid values are 0.0 to 1.0, inclusive.

The number of bits examined for the pretrigger BER which is used for comparison to the **BER trigger threshold**, is determined by the specified **confidence** and BER trigger threshold values. The following images show the range of required input lengths for a **confidence** input in the range [0.5,0.99] and a **BER trigger threshold** input in the range [0.1,0.5].

**Default: **0.1

Level of confidence that the actual BER of the bits following a trigger will be below the specified **BER trigger threshold**. Values between 0.0 and 1.0 represent proportional confidence.

The specified **confidence** can only be reached after processing a minimum number of bits in the **input bit stream**. This parameter indirectly specifies the minimum **input bit stream** length in which a trigger can occur. Specify a **confidence** value of -1 to allow triggering on **input bit stream** lengths equal to 3 × (*PN sequence order*).

**Default: **0.95

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an **error in** input and an **error out** output so that the node can respond to and communicate errors that occur while code is running. The value of **error in** specifies whether an error occurred before the node runs. Most nodes respond to values of **error in** in a standard, predictable way.

**Default: **No error

The measured BER as the ratio of erroneous bits to the bits following a trigger in the current **input bit stream**.

The number of bits considered for this measurement depends on the conditions shown in the following table.

The measured bit error rate as the ratio of erroneous bits to bits following a trigger.

The number of bits considered for this measurement depends on the conditions shown in the following table.

A Boolean that indicates whether the node found a trigger.

When **trigger found?** is TRUE, the trigger was found in the **input bit stream**. When **trigger found?** is FALSE, the trigger was found in the current or a previous **input bit stream**.

The index value of the first bit where the bit pattern matched the specified PN sequence.

This index value indicates the number of bits since the last reset that are not PN data. For example, if the transmitter is off for 30 bits, this parameter returns 30.

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

**error in** input and an **error out** output so that the node can respond to and communicate errors that occur while code is running. The value of **error in** specifies whether an error occurred before the node runs. Most nodes respond to values of **error in** in a standard, predictable way.

The minimum number of input bits required to return a meaningful BER value is given by

${{N}_{\mathrm{min}}=\mathrm{int}\left(\frac{\sqrt{y\times threshold\times (1-threshold)+120\times threshold}+\sqrt{y\times threshold\times (1-threshold)}}{2\times threshold}\right)}^{2}$

where

*y* is defined such that confidence=P(x≤y)

*x* is a zero-mean, unit-variance Gaussian variate

*P(x≤y)* denotes the probability that the variable *x* takes a value that is less than or equal to *y*.

The **BER trigger threshold** input triggers this node, meaning that the node only reports BER on bits after a match is found. Hence, you do not need to synchronize your transmitter with your unit under test (UUT)—the test can begin before transmission begins.

**Where This Node Can Run: **

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application