RFUnderstanding Single Ended BER (SBER) Test Failures
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Let’s break down what an SBER (Single Ended Bit Error Rate) test is, especially when it fails in equipment like a CMU200. As you know, BER stands for Bit Error Rate.
What is BER?
Basically, a BER test checks how accurately data is transmitted. It compares the bits that were sent to the bits that were received after decoding. The formula is straightforward:
In a typical loopback BER test, the tester (like a CMU200) sends a pseudo-random data sequence (like PN9 or PN11) after processing it according to a wireless standard, such as GSM, to the device under test (UE or mobile). The CMU200, in this case, includes the physical layer transmitter.
The UE receives this GSM-compliant signal and decodes it. This decoded data is then sent back through the uplink physical layer chain to the tester (CMU200). The tester then compares the original transmitted sequence with the looped-back data, calculates the BER, and shows it on the screen. This is often called a double-ended BER test.
Single Ended BER (SBER) Explained
Unlike the loopback method, single-ended BER (SBER) doesn’t loop the decoded data back through the uplink physical layer. Instead, the UE (Mobile) is responsible for comparing the decoded data (call it ‘B’) with the original PN sequence (‘A’) that the tester (CMU200) sent. The UE then reports the SBER result back to the CMU200 for display.
Crucially, in an SBER test, the CMU200 doesn’t compare any data. It simply transmits the data and receives the BER result from the UE.
Why Use SBER?
This SBER test is excellent for assessing the DUT’s (Device Under Test) receiver sensitivity without needing to loop the data back. The advantage is that the tester doesn’t need uplink signal processing capabilities.
The tester (CMU200) only needs the downlink physical layer signal processing chain, which the DUT will process. The tester and DUT can comply with standards like GSM, CDMA, or LTE. They can even be WLAN or WiMAX devices.
