Need help on determine receiver SNR

Dear community.

I'd like to design the DBPSK tranceiver that adapt from this example Top-Down Design of an RF Receiver - MATLAB & Simulink (mathworks.com)

Here is my design specifications.

Data rate = 600 bps

Each packet 200 bits long

DBPSK modulation

Recerver Sensitivity = -126 dBm

Packet Error rate (PER) 10e-6

Now I am on the step that determine the receiver SNR requirement.

My problem is when trying to do Error Rate Calculation, BER is always 0.5 (50%) of the transmitt packet.

Could you guys help to have a look why I always BER like this?

Here is what parameter I set for each block. (Only changed parameters is mentioned)

Bernoulil Binary Generator

• Sample time = 1/600
• sample per frame = 200

Raised Cosine Transmit Filter

• Rolloff factor = 0.05
• Filter span in symbols = 10
• Output sample per symbol = 2
• Input processing = frame based

Raised Cosine Receive Filter

• Rolloff factor = 0.05
• Filter span in symbols = 10
• Input sample per symbol = 2
• Decimation factor = 2
• Input processing = frame based

Dealy

• Delay length = 10 (Txfilterspan/2+Rxfilterspan/2)

Error Rate calculation

• Receive Delay = 10

I also attached the Simulink work space for your reference.

Best Regrads,

Fumihiko Sato

Answer 1

[Gokul Nath S J]

Hi Fumihiko Sato,

Based on your query, it seems that the bit error is fixed at 0.5. Even if the other quantities are changed, still the bit error is constantly converging to 0.5.

As per my observation, I found that the error rate is converging to the probability of one/zeros that you input. Ideally it should not. If you change the probability of zero to a different value and then run the code, the Bit error will try to converge to that point. So the delay should be properly taken care since the block error rate calculation is carried out with random 1s and 0s as the convergence makes it clear.

with regards,

Gokul Nath S J