BER (Bit Error Rate)
The Bit Error Rate (BER) is a metric used to indicate how often a packet or other data unit has to be retransmitted because of an error.
In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion, or bit synchronization errors.
The bit error rate (BER) is the number of bit errors per unit of time. The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval.
As an example, assume this transmitted bit sequence:
1 1 0 0 0 1 0 1 1
and the following received bit sequence:
0 1 0 1 0 1 0 0 1
In this case, the number of bit errors (the underlined bits) is 3. The BER is 3 incorrect bits divided by 9 transferred bits, resulting in a BER of 0.333 or 33.3%.
What Causes Bit Errors?
In a communication system, the receiver side BER may be affected by transmission channel noise, interference, distortion, bit synchronization problems, attenuation, wireless multipath fading, etc.
In wireless fibre optics (laser communications), the BER may be affected by scintillation, vibration, and line-of-sight obstructions.
Testing for BER
A bit error rate test (BERT) is a testing method for digital communication circuits that uses predetermined stress patterns consisting of a sequence of logical ones and zeros generated by a test pattern generator.
A BERT typically consists of a test pattern generator and a receiver that can be set to the same pattern. They can be used in pairs, with one at either end of a transmission link, or singularly at one end with a loopback at the remote end. BERTs are typically stand-alone specialized instruments, like a Viavi tester. During the test the number of errors, if any, is counted and presented as a ratio such as 1 in 1,000,000, or 1 in 1e06 (1E-06).
The bit error rate is never constant, especially for a wireless link. For CENTAURI, link degradation due to line of sight obstructions, vibration, and scintillation will impact the BER.
What Is Considered An Acceptable BER?
It is virtually impossible to reduce Bit Error Rates to 0. Sensitivity to Bit Errors and the impact to the end-user experience will also vary widely by use case.
For wireless laser communications, the table below describes the link performance level given a certain BER.
1E–05= 1 x 10^-5= 0.00001
1E–08= 1 x 10^-8= 0.00000001
Does BER Matter to Me?
Again, your mileage may vary, and BER will change in response to many factors.
For internet service links, higher BERs mean that more retransmissions of data packets are required (TCP/IP) to send and receive data successfully.
For data-intensive use cases like media streaming, file transfers, and other forms of content delivery, the end-user or client experience is rarely affected by BER as retransmissions are handled by the switching and routing systems handling the transmissions at levels above Layer 1.
However, if there is a high BER for applications involving real-time communications, signalling data and mobile voice calls, the client experience will suffer as BERs increase. In these situations, BERs >1E-05 will reduce the quality of the end-user experience.
How Can I Minimise Bit Errors?
In many wireless communications systems, if the BER is too high, modulating to a slower data rate may actually improve overall transmission time for a given amount of transmitted data. This is a common method for improving performance in many RF and Microwave systems.
For Wireless Laser Communications, systems must use other means to address Bit Error Rates. As a Layer 1 communications device, CENTAURI utilises Adaptive Power Control, coupled with a highly responsive Positioning, Alignment, and Tracking (PAT) system to adapt and maintain the quality of the connection between linked devices.
This, coupled with the proper configuration of the switches and routers to which CENTAURI devices are connected helps maintain the quality of service and acceptable Bit Error Rates for most applications.
Some applications remain highly sensitive to any change in BER and Transcelestial is pioneering work in addressing the requirements of these use cases with a new generation of "Hybrid High Availability" solutions, combining the high data throughput capabilities of CENTAURI with the (sometimes) more reliable but slower transmission speeds of traditional RF and Microwave equipment.
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