MT Calculate BER VI

LabView Digital Modulation

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MT Calculate BER VI

Calculates the average bit error rate (BER) against a PN sequence or user-specified reference bit pattern.

Use the pull-down menu to select an instance of this VI.

MT Calculate BER After Trigger (Fibonacci PN Sequence)

This polymorphic instance calculates the average BER against a Fibonacci PN sequence. The sequence must be the same as the PN sequence generated by the Fibonacci instance of the MT Generate Bits (poly) VI with a matching PN order.

On first call, or whenever reset? is TRUE, the VI 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 VI 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 VI use a continuation of the same PN sequence until reset? is set to TRUE.

MT Calculate BER After Trigger (Fibonacci PN Sequence)

input bit stream specifies the bit sequence over which BER is calculated. This bit stream should include only data bits of the PN sequence.

Note To avoid faulty triggering caused by synchronization and/or guard bits, NI recommends that the input bit stream be a phase-continuous PN sequence such as that generated by the MT Generate Bits (poly) VI.

PN sequence order specifies 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 between 5 and 31. The default is 9.

BER trigger threshold specifies the BER threshold that must 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 between 0.0 and 1.0. The default is 0.1.

Note The number of bits examined for the pretrigger BER 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].

confidence specifies the level of confidence that the true 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. For example, a value of 0.95 (default) specifies 95% confidence. The default is 0.95 (95% confidence).

Tip Specify a value of -1 to set the minimum number of bits required for a trigger to the length of the specified reference bit pattern. This option is useful when the input bit stream is very short.

Note The specified confidence can only be reached after processing a minimum number of bits in the input bit stream. As such, 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).

reset? specifies whether the VI continues bit error rate calculations from a previous iteration. Set reset? to TRUE to reset the trigger and the accumulated BER measurement. A reset? setting of FALSE maintains the previous synchronization and does not clear the existing accumulated BER value. The default is TRUE.

error in (no error) can accept error information wired from previously called VIs. Use this information to decide if any functionality should be bypassed in the event of errors from other VIs. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

	status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	code identifies the error or warning code. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

BER returns the measured bit error rate as the ratio of erroneous bits to 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.

Scenario	Conditions	BER Output
1.	reset? set to TRUE or first call, and trigger not detected in the current input bit stream	1.0
2.	reset? set to FALSE, and trigger not detected in the current input bit stream, or trigger not detected in previous calls to the same instance of this VI	1.0
3.	reset? set to TRUE or first call, and trigger detected in the current input bit stream	BER calculation based on the length of bits following the set of N + 1 bits in which the trigger was detected, where N is the specified PN sequence order
4.	reset? set to FALSE, and trigger detected in previous calls to the same instance of this VI	BER calculation based on the length of the input bit stream

accumulated BER returns 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 in the following table.

Scenario	Conditions	BER Output
1.	reset? set to TRUE or first call, and trigger not detected in the current input bit stream	1.0
2.	reset? set to FALSE, and trigger not detected in the current input bit stream, or trigger not detected in previous calls to the same instance of this VI	1.0
3.	reset? set to TRUE or first call, and trigger detected in the current input bit stream	BER calculation based on the length of bits following the set of N + 1 bits in which the trigger was detected, where N is the specified PN sequence order
4.	reset? set to FALSE, and trigger detected in previous calls to the same instance of this VI	Accumulated BER calculation based on the length of the input bit stream.

trigger found? returns whether the VI 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.

trigger found index (bits) returns 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 out passes error or warning information out of a VI to be used by other VIs. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

	status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	code is the error or warning code. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	source describes the origin of the error or warning. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

MT Calculate BER After Trigger (PN Sequence)

This polymorphic instance calculates the average BER against a Galois PN sequence. The sequence must be the same as the PN sequence generated by the Galois instance of the MT Generate Bits (poly) VI with a matching PN order. All subsequent iterations of the VI use a continuation of the same PN sequence until reset? is set to TRUE.

MT Calculate BER After Trigger (PN Sequence)

input bit stream specifies the bit sequence over which BER is calculated. This bit stream should include only data bits of the PN sequence.

	status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	code identifies the error or warning code. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

Scenario	Conditions	BER Output
1.	reset? set to TRUE or first call, and trigger not detected in the current input bit stream	1.0
2.	reset? set to FALSE, and trigger not detected in the current input bit stream, or trigger not detected in previous calls to the same instance of this VI	1.0
3.	reset? set to TRUE or first call, and trigger detected in the current input bit stream	BER calculation based on the length of bits following the set of N + 1 bits in which the trigger was detected, where N is the specified PN sequence order
4.	reset? set to FALSE, and trigger detected in previous calls to the same instance of this VI	BER calculation based on the length of the input bit stream

Scenario	Conditions	BER Output
1.	reset? set to TRUE or first call, and trigger not detected in the current input bit stream	1.0
2.	reset? set to FALSE, and trigger not detected in the current input bit stream, or trigger not detected in previous calls to the same instance of this VI	1.0
3.	reset? set to TRUE or first call, and trigger detected in the current input bit stream	BER calculation based on the length of bits following the set of N + 1 bits in which the trigger was detected, where N is the specified PN sequence order
4.	reset? set to FALSE, and trigger detected in previous calls to the same instance of this VI	Accumulated BER calculation based on the length of the input bit stream.

	status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	code is the error or warning code. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	source describes the origin of the error or warning. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

MT Calculate BER After Trigger (User Pattern)

This polymorphic instance calculates the average BER against a user-defined sequence. The sequence input in the input bit stream array must be the same as the sequence specified in the reference bit pattern control.

On first call, or whenever reset? is TRUE, the VI attempts to locate a trigger within the input bit stream by comparing it to the reference bit pattern under the constraints set by the confidence and BER trigger threshold parameters. When the BER on the subsequent input bits is below the specified threshold over the number of bits specified by confidence, the VI begins reporting the BER.

MT Calculate BER After Trigger (User Pattern)

input bit stream specifies the bit sequence over which BER is calculated. This bit stream should include only data bits of the PN sequence.

reference bit pattern user-defined sequence defines the bits that are compared to the input bit stream to calculate BER and accumulated BER. When this function is reset, the starting bit of this sequence is adjusted to find the minimum BER

	status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	code identifies the error or warning code. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

Scenario	Conditions	BER Output
1.	reset? set to TRUE or first call, and trigger not detected in the current input bit stream	1.0
2.	reset? set to FALSE, and trigger not detected in the current input bit stream, or trigger not detected in previous calls to the same instance of this VI	1.0
3.	reset? set to TRUE or first call, and trigger detected in the current input bit stream	BER calculation based on the length of bits following the set of N + 1 bits in which the trigger was detected, where N is the specified PN sequence order
4.	reset? set to FALSE, and trigger detected in previous calls to the same instance of this VI	BER calculation based on the length of the input bit stream

Scenario	Conditions	BER Output
1.	reset? set to TRUE or first call, and trigger not detected in the current input bit stream	1.0
2.	reset? set to FALSE, and trigger not detected in the current input bit stream, or trigger not detected in previous calls to the same instance of this VI	1.0
3.	reset? set to TRUE or first call, and trigger detected in the current input bit stream	BER calculation based on the length of bits following the set of N + 1 bits in which the trigger was detected, where N is the specified PN sequence order
4.	reset? set to FALSE, and trigger detected in previous calls to the same instance of this VI	Accumulated BER calculation based on the length of the input bit stream.

trigger found? returns whether the VI found a user-defined sequence synchronization that exceeded the specified BER trigger threshold.

trigger found index (bits) returns the index value of the first bit where the bit pattern matched the specified user-defined pattern. This index value indicates the number of bits since the last reset that didn't contribute to the BER calculation did not exceed the value specified by threshold. For example, if the transmitter is off for 30 bits, this parameter returns 30.

	status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	code is the error or warning code. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.
	source describes the origin of the error or warning. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error.

Details

For MT Calculate BER After Trigger (PN Sequence) VI

Note While stepping through the input bit stream one bit at a time, this VI attempts to locate a trigger using the following procedure:

Length-checking the input bit stream (minus any bits already examined in previous attempts to find a trigger). If the available length is insufficient to meet the specified confidence, the VI buffers input bits and exits without locating a trigger.
Generating a trial PN sequence seed (trial seed) based on the next N + 1 bits, where N is the expected PN sequence order. Generating a trial PN sequence based on the trial seed, with a length of the specified confidence.
Calculating a trial BER value using the trial PN sequence as a reference and comparing this reference to the bits following the N + 1 bits that generate the trial seed. The VI returns to step 1 if the trial BER is above the specified BER trigger threshold.
Generating a second trial PN sequence seed, using the N + 1 bits immediately following the N + 1 bits used to generate the first trial PN sequence seed. Generating a trial PN sequence based on the trial seed with a length of the specified confidence - (N + 1) bits.
Calculating a trial BER value using the trial PN sequence as a reference and comparing this reference to the bits following the N + 1 bits used to generate the trial seed. The VI returns to step 1 if the second trial BER is above the specified BER trigger threshold.
Returning a trigger found? value of TRUE.

BER calculation begins on the bit following the first set of N + 1 bits in which the trigger is found.

The VI is triggered, meaning that the VI 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. The trigger found? parameter returns whether the BER measurement has started. When reset? is set to FALSE, the trigger found index parameter returns the starting bit for the block of data in which the trigger initially occurred (this is not necessarily the current block).

On first call, or whenever reset? is TRUE, the VI begins a blind search over the input bit stream for a trigger found index location in which the BER of a number of subsequent bits is below the specified BER trigger threshold. The confidence parameter specifies the number of bits after the trigger found index that are used in the trigger threshold calculation.

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