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Part Number: CC1120
We'd made some communication tests with CC1120 recently.
We tried several communication baudrate and found that at different baudrate it is better to use different preamble length. When preamble length was wrong, packet loss will happen.
The configuration of our system is as below:
The preamble length 4 Bytes seems to be the best.
The preamble length 12 Bytes seems to be the best.
Longer preamble means more protocol overhead, hence we want to get the minimum usable preamble length.
What is related to the preamble length configuration?
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In reply to M-W:
Do you have a table that summarize your findings?
Have you tested with different values for AGC_WIN_SIZE?
Most of our testing has been done with 4 byte preamble meaning that we haven't looked into performance vs preamble length.
In reply to TER:
At first we used the setting export from SmartRF Studio.
The BaudRate is 76.8Kbps.
Then we changed the setting to this.
We had made the test at different time and with different terminal, got the same result.
We also readed the SWRU295E - CC112X/CC1175 Low-Power High Performance Sub-1 GHz RF Transceivers/Transmitter Page 38 and calculated the time by DN510_CC112X_RSSI_and_CS_Response_Time_Calculation_Sheet.
When AGC_WIN_SIZE=128 sample
AGC Hold = 335.0 us, it means 25.73 bits at 76.8 Kbps
AGC STABLE = 697.88 us, it means 53.60 bits at 76.8 Kbps
Does it mean we need longer preamble length + sync word size?
When the sync word size is fixed 16 bit, does it mean we need the preamble length be longer than 4 bytes?
In reply to kinyanderson:
- How are these tests done?
- What does the AGC FE Gain min/ max mean? In general, could you explain what the different columns are? It's not clear.
- If you need CS you need to adjust the preamble length (not the sync word) according to the equations in the app note.
We used 2 pieces of CC1120, one act as transmitter and the other as receiver, and tried different settings.
AGC FE Gain is the value we read from this reg. We tried to learn how AGC behave. Then we got the min and max value at each input level.
We also found that the RSSI value would jitter within a large range when AGC_WIN_SIZE was set to a small value. Hence we had to choose a big value in order to get more stable RSSI value.
When AGC_WIN_SIZE was set to a bigger value, it's better to use a longer preamble length, or else the packet loss would happen at some input level.
Are you able to do conducted tests?
The reason I ask is that when finding settings you should do this conducted meaning that a signal generator should be connected directly to the DUT. When you test radiated you may get in noise etc that is not relevant at this stage. First you should get good performance conducted and then start radiated testing.
To find optimal settings are also a bit with trial and error since it's not possible to write equations that cover all permutations of settings.
Thanks. We'll try it later.
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