As written in the manual, I can get RI (Rank Indicator) by the following AT command.
+QNWCFG: "lte_csi",1,1,0,0 # RI=1
Also, although not written in the manual, RM500Q accepts AT command
+QNWCFG: "lte_mimo_layers",0,2 # Layer=2
It seems the rank value from those two AT commands above are mostly the same value, but sometimes different values. What is the difference and meaning of the each values?
Also, similar AT commands for 5G NR:
My firmware: RM500QAEAAR13A02M4G_01.001.01.001
lte_csi and lte_mimo_layers is two different concepts.
The RI is the effective number of data layers for PDSCH, queried by lte_csi, it is a mathematical meaning, is a value obtained by matrix operations. RI refers to determining the number of available transmission channels on each connection link in the MIMO system. The range of RIs is usually related to MIMO configurations, for example, RI=1 for single-antenna transmission and RI=2 for dual-antenna transmission.
The number of downlink/uplink MIMO layers queried by lte_mimo_layers. MIMO is a wireless communication technology that transmits and receives data by using multiple antennas at the same time. Common MIMO configurations are 2x2, 4x2, 4x4, etc., which means that the transmitter and receiver have 2 and 4 antennas, respectively.
MIMO and RI are correlated in LTE networks, but they are not the same concept. MIMO is a technical means to improve wireless communication performance through the use of multiple antennas. RIs are used to tell the receiver how many antennas should be used for data transmission in a given MIMO configuration.
As for MIMO is 2 and RI is 1, This is normal may because of:
MIMO supported but not fully utilized: Some devices or base stations in LTE networks may have multiple antennas and MIMO-enabled features, but for some reasons (such as network congestion, poor signal quality, etc.), it is not possible to utilize all antennas for data transmission at the same time. In this case, the MIMO configuration is still 2x2, but only one of the antennas can be utilized for transmission, i.e. RI is 1.
MIMO adaptability: LTE networks use MIMO adaptive technology to dynamically select the appropriate MIMO configuration based on current channel conditions and system load. When the channel quality is poor or the network is congested, the system may automatically reduce the level of MIMO to improve the success rate of transmission. In this case, a MIMO configuration of 2x2 and RI setting of 1 may be chosen to better adapt to the network environment under harsh channel conditions.