Bit Error Rate (BER) Test and Measurement Using BER Meter

Bit Error Rate (BER) testing is a crucial aspect of evaluating the performance of digital communication systems. It involves measuring the rate at which errors occur in a transmitted bitstream compared to the expected bitstream at the receiver end. The BER measurement helps in assessing the quality and reliability of the communication link, which is essential for ensuring the proper functionality of digital communication systems.

Let’s understand Bit Error Rate (BER) test and measurement using a BER meter in a test setup and explore alternative BER measurement methods, such as the XOR method and the FPGA method.

What is Bit Error Rate (BER)?

As we know, BER stands for Bit Error Rate. It is the ratio of the number of bits received in error compared to the total number of bits transmitted.

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Refer to BER Basics, which describes BER and mentions the setup used to measure BER in the following two scenarios:

• VSAT system with satellite
• VSAT to VSAT via satellite

BER Test Setup Using BER Meter

A BER meter is a specialized instrument used to measure the Bit Error Rate. It’s often employed in BER testing setups to automate the process of error detection and calculation.

Before starting the test, the BER meter needs to be calibrated and initialized according to the specifications of the communication system being tested. This may involve setting parameters such as the data rate, modulation scheme, signal levels, etc.

Figure-1: BER test setup

Figure 1 depicts a simple BER test setup.

Usually, a BER meter such as the HP 4951C protocol analyzer is used for measurement. A BER test tool like this is sufficient to test the BER of any system.

The BER meter counts the number of bit errors detected during a specific period or for a specific number of transmitted bits. This count is crucial for calculating the BER.

The following steps are performed for BER measurement using a BER meter:

• STEP-1: Connect the output of the BER meter, which generates a PRBS (Pseudo-Random Binary Sequence), to the input of the transmitter. If required, a provision needs to be provided to disconnect the binary source and connect the output of the BER meter. This is shown in the figure.
• STEP-2: Connect the output of the receiver (i.e., binary data) back to another input port of the BER meter.
• STEP-3: The BER meter compares the output and input binary sequences and determines the BER, displaying the result.

To measure the stability of the prototype system, BER measurement is usually run for 3 days (for short-term stability) or for 40 days (for long-term stability).

• For Software Code or prototype hardware with a provision to tap binary source data, the BER is calculated by comparing the delayed version of the input binary source and the decoded binary pattern of the receiver part. This calculation can be done using code written on DSP, FPGA, or in any language (C, C++, MATLAB, Labview, etc.) as per requirement.

Other BER Measurement Methods | XOR Method, FPGA Method

In addition to using a dedicated BER meter, there are alternative methods for measuring Bit Error Rate (BER) in digital communication systems. Two such methods are using XOR (Exclusive OR) and FPGA (Field-Programmable Gate Array).

Let’s explore each method:

XOR Method

• Principle: In the XOR method, the received data stream is compared with the transmitted data stream using an XOR operation. XOR compares two binary inputs and outputs a 1 if the inputs are different and a 0 if they are the same.

• Implementation:

  1. The transmitted and received data streams are fed into the inputs of an XOR gate.
  2. The output of the XOR gate indicates where the two streams differ, implying a bit error.
  3. Counting Errors: By counting the number of 1s in the XOR output, you can determine the number of bit errors.
  4. Calculation: The BER can then be calculated using the formula mentioned earlier:

  $BER = \frac{\text{Number of Bit Errors}}{\text{Total Number of Transmitted Bits}}$

FPGA Method

• Principle: Field-Programmable Gate Arrays (FPGAs) are programmable hardware devices capable of implementing digital circuits. In this method, FPGAs are utilized to perform real-time BER testing and measurement.
• Implementation:
  1. The FPGA is programmed to act as both a transmitter and a receiver.
  2. The transmitted data is generated within the FPGA and then sent through the communication channel.
  3. At the receiver side, the FPGA captures the received data and compares it with the original transmitted data.
  4. The FPGA counts the number of errors and calculates the BER internally.

Conclusion

Overall, BER testing using a BER meter in a test setup is a fundamental technique for evaluating the quality and reliability of digital communication systems, ensuring they meet the required performance standards. While dedicated BER meters offer convenience and accuracy, XOR and FPGA methods offer simpler or more customizable solutions, respectively, for specific testing scenarios.

BER Measurement Equipment Vendors

The popular BER equipment vendors include Tektronix, Keysight Technologies, Anritsu, Fluke Networks, Lecroy, etc. Refer to the complete list of companies manufacturing BER T&M Equipments.