I am a software developer who knows a bit about electronics and very little about RF. I am trying to understand how to interpret the various signal strength and quality values which can be obtained from the SARA R410M-02B (NovaM). Of course, this topic is not specific to any particular module…
Okay, the three measures that I routinely see (and the NovaM) can provide are:
RSSI: Received Signal Strength Indication (expressed in dBm, decibels/milliwatt)
RSRP: Reference Signal Received Power (expressed in dBm)
RSRQ: Reference Signal Received Quality (expressed dB)
Since I do not understand the nature of any of those measures, please correct me where I am incorrect…
RSSI is more general than RSRP in that RSRP is LTE specific and RSSI is a measure which is also meaningful regarding GSM (and other) technologies.
RSSI and RSRP are both indicating the strength in some way of the signal measured at the antenna.
RSRQ is a measure of signal “quality.” I don’t really know what that means.
I notice that RSSI and RSRP generally “move together.” That is, when RSSI goes up/down from one reading to another, RSRP tends to move in the same direction.
This is not the case for RSRQ. RSRQ may go up from one reading to another while RSSI/RSRP move in the same or opposite direction.
I suspect that RSRQ is affected by traffic. That is, with more network demand RSRQ may go down, regardless of signal strength (RSSI/RSRQ). Is this correct?
I’ll be very grateful if someone who really understands this subject to offer a bit of education.
RSSI is more general than RSRP in that RSRP is LTE specific and RSSI is a measure which is also meaningful regarding GSM (and other) technologies.
Not really, RSSI is formally defined for 2G-LTE where RSRP is only formally defined for LTE but the principals are present in all RF technologies. (Same with RSRQ).
RSSI and RSRP are both indicating the strength in some way of the signal measured at the antenna.
Checkout the link for the details but basically RSSI is wider band and includes neighboring carriers and noise. Think of RSSI like the noise level within a crowded room where you are trying to talk to someone. It includes the noise the person you are interested in hearing is making but also the background communication and other noises. RSRP is a more accurate measure of how loud the person you are interested in hearing is speaking basically a measure of how loud the “interesting” audible noise is.
RSSI and RSRP are both indicating the strength in some way of the signal measured at the antenna.
Yes, see above, and as you mentioned reported in dBm which is a unit of power
RSRQ is a measure of signal “quality.” I don’t really know what that means.
RSRQ, as you mentioned in reported in dB which is a unitless ratio (in this case Power / Power). It is somewhat like signal to noise ratio although see the link for more details about this.
I notice that RSSI and RSRP generally “move together.” That is, when RSSI goes up/down from one reading to another, RSRP tends to move in the same direction.
Yes since both are measuring received power, RSSI includes the power measured in RSRP. So you cant really have a high RSRP with a low RSSI. You theoretically could have a low RSRP with a high RSSI if you are being jammed or in other laboratory conditions.
This is not the case for RSRQ. RSRQ may go up from one reading to another while RSSI/RSRP move in the same or opposite direction.
Hopefully this makes more sense to you know, RSRQ is more like SNR which can be independent of received Power. Basically you can have an SNR of 1 with a quiet person in a quiet room or a loud person in a loud room.
I suspect that RSRQ is affected by traffic. That is, with more network demand RSRQ may go down, regardless of signal strength (RSSI/RSRQ). Is this correct?
I would say RSRQ is likely more affected by congestion than traffic, but overall sure. You and 1 other person can share the same cell tower and they could be sending / receiving a massive amount of data but if the tower is scheduling your time slices far away or on significantly different frequencies then it wont really matter. If a tower has to maintain many connections then the frequency bands and time slices will likely be fully utilized meaning many other devices are transmitting or receiving at the same time and on the same frequencies as you are. Im not 100% sure about this but based on my understanding I think that makes sense.