Sim800 FCC Testing for GPRS

Question

I have created a small product using Sim800 and the product uses only GPRS. I am told by the testing company, that I need to create a test firmware which will continuously transmit. The confusion is, that in order to continuously transmit, I need to know which IP and port to connect, but the testing house says, it will be simulated...and I don't understand what does that mean. Even after 3 calls, the testing house keeps repeating the same requirement.

Maybe, either I'm not asking the right question or the testing house is not giving me right answer.

Therefore, the exact question is - I need to write a firmware which will use AT commands of Sim800, connect to the internet and simply ping a website in a loop. Since this will be inside a simulator, what IP/Port combination is required OR how is this simulated.

The testing house does not say anything and is not very co-operative in this regard.

Any pointer in this area would be of great help.

Answer 1

The "continuous transmission" requirement cannot be met with regular HTTP requests, you are expected to use every GSM slot, ignoring any higher-level protocols.

This test verifies that the emission spectra are within required parameters; this is done by moving a bandpass filter across the spectrum and writing down the power of the signal received. As moving this filter requires some time, the signal must be present for the entire duration -- interruptions could hide problems.

You are still required to follow the GSM framing and disable the amplifier between packets to verify that the sharp transitions at the packet boundaries do not translate to transmissions outside the allowed range.

The module is already approved as far as I know, so there is most likely a non-functional testing variant of the firmware that was used in that certification, so you'd have to ask the vendor for either a copy of that firmware, or a pre-flashed module that can be used for verification.

Answer 2

I found the answer to this question. The test lab will have a "mobile tower" simulator (one example is R&S CMU 500 simulator model). The simulator will create a "mobile tower" scenario in an anechoic chamber. In order to connect to a GPRS network, you need to first "attach to GPRS". Now this is done via (generally) AT command (e.g. AT+CGATT). Then, you need to specify the APN, UID and PWD. In my case, the simulator accepts any APN, so, the actual value was not important. After that, you will be given two options ; your device can act like a client or like a server. Your device generally gets an IP address assigned by the simulator. If you design your device like a server, then the simulator will ping your device. Alternatively, if your device acts like a client, you will be given an IP address / port number combination that your device can ping. What you need to remember is make your test firmware in such a way, that the IP/port can be configured during testing. Do not hardcode. Also, during testing, you need to continuously transmit. The process to specify APN, connect to a remote server or act like a server is completed using AT commands. Each module may have its own AT command set to do this, so check the module AT command datasheet.

Please note, the lab will provide you a SIM card and we were not allowed to use our own SIM card.

For specific around IP/port, talk to your test lab and they should give you the parameters. Hope this helps others too.