Evaluation of LTE signal quality

[danielm]

We would like to implement LTE signal quality reporting in our products. Which LTE radio parameters are most relevant and how to interpret them?

E.g. command 'AT!="showphy"' returns following statistics:

DL SYNCHRO STATISTICS
=====================
    Synchro state                         : DRX_SLEEP
    PPU SIB1 ACQ watchdog                 : 0
    Frequency Hypothesis RF  (Hz)         : 0
    RSRP (dBm)                            : -82.43
    RSRQ  (dB)                            : -11.18
    Channel estimation state (Cell-spec.) : HIGH CINR
    Channel estimation state (UE-spec.)   : LOW CINR
    Channel estimation state (MBSFN)      : LOW CINR
    Channel estimation CINR               : 19.00
    Channel length                        : SHORT
  AGC
    AGC RX gain (dB)                      : 44.79
    RX PSD BO (dBFs)                      : -21.21
    RX PSD (dBm)                          : -85.27
    Noise level RS (dBm)                  : -100.49
    Digital gain (dB)                     : 3.68
    CINR RS (dB)                          : 18.06
  NARROWBANDS
    Last DL NB                            : Central
    Last UL NB                            : 0
  AFC
    Frequency offset RF  (Hz)             : -376
    Frequency offset BB  (Hz)             : 0
  PBCH
    MIB received quantity                 : 0
    MIB timeout quantity                  : 0

Command 'AT+CESQ' reurns "not known or not detectable" for rxlev (Received signal strength level), ber (Channel bit error rate), rscp (Received signal code power) and ecno (Ratio of the received energy per PN chip to the total received power spectral density). Quality parameters rsrq (Reference signal received quality) and rsrp (Reference signal received power) are determined.

+CESQ: 99,99,255,255,17,58

[Chris Williams]

@danielm Did you ever get an answer to WHY 'AT+CESQ' fails to return:
RECEIVED SIGNAL STRENGTH LEVEL
CHANNEL BIT ERROR RATE
RECEIVED SINGAL CODE POWER
RATIO OF RECEIVED ENERGY

i.e. the first 4 parameters in the command?

[kjm]

Anything down to -12dBm is usually OK

[danielm]

@kjm
How exactly do you usually interpret RSRQ values from range -3 to -20dB?
In a table available in the following link RSRQ < -11dB is considered to indicate poor signal quality:
http://usatcorp.com/faqs/understanding-lte-signal-strength-values/

Attach/connect time relation with link quality is quite interesting.

[kjm]

I like to use RSRQ because it's known range (-3 to -20) makes it easy to filter out bogus values. The big problem is that connection reliability & data rate usually has a lot more to do with tower loading than signal strength. Often how long it takes to attach & connect says a lot more about what sort of data session your likely to have.