General Questions about the MC7455

Dear all,

I have some general question about the MC7455, and I hope to find the answers here.

The first one is regarding the SNR measurement: When I get the information about the link from the modem, it displays something similar to “SNR = 21dB”. After checking with the LTE standard, it seems that LTE modems should not really measure the SNR but rather the SINR (Signal to Interference Noise Ration). Also from the measurements, that I have done, I think that there is no way that this value is pure SNR. So am I right in assuming that SINR is really being measured by the modem, and it is displayed as SNR when you query the signal info ?

The second question is about the RSSI measurement: I have noticed that when the modem is at the Cell Edge it will sometimes display a “0dbm” value for the RSSI. When out of coverage it shows an error when being prompted for signal information. Am I right in assuming that the modem will give the “0dBm” value when something fishy has happened? (for example invalid value or signal was too low to measure correctly but not low enough to detect loss of coverage, i assume the modem detects the signal but the data that comes is corrupted due to poor SNR and bit error)

Regards

Georgi

Georgi,

Can you post the commands/responses you are seeing/using so that we can actually see the figures you are talking about?

Regards

Matt

Hi Matt,

Thank you for the response. Unfortunately not, because I am not working directly with the modem, but with a proprietary cisco based gateway that interfaces with the modem. What i do is, I ssh into the gateway via VM and request signal quality information from the router (Basic Cisco SSH Query). We a collaborating together on a project with the company, that developed the gateway, but they refuse to send us any inside information about how they have implemented the communication between the modem and the gateway. Anyway, I am pretty sure that the do not calculate these values themselves, but take them directly from the modem. And that is why I decided to ask here how exactly does the modem measure such parameters (RSSI, RSRQ, RSRP, ECIO ect.) It is more of a general question than a question, rather than a question related to a specific technical issue. I am just trying to figure out the reason for a couple of measurement results.

Regards
Georgi

Georgi,

All of the values you mention are directly available through AT commands and/or QMI API’s depending on how the third party company is using the unit. How thy present the information that is available to the outside world is up to them.

Regards

Matt

Hi Matt,

Thank you very much for the answer you provided. I will try to talk with them on the matter.

Regards

Georgi