Evaluating Your Signal - Digi TransPort WR21 Handbook

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Evaluating Your Signal

In 2G and 3G networks, signal strength was best understood using the received signal strength indicator (RSSI),
measured in dBm. That value alone only provides a measure of the total signal including noise, and, of course,
noise degrades the performance of a cellular connection. For example, a cellular router installed in an electric
substation may pick up a strong cellular signal – but it will still perform poorly due to electromagnetic interference.
That's why it's important to understand not only the strength of the signal, but also its quality.
Most 2G/3G CDMA and WCDMA (i.e., UMTS/HSPA) devices also report Ec/Io which is a better indicator of signal
quality. However, this metric is less commonly used and not as well understood as RSSI.
For 3G cellular connections, RSSI and Ec/Io determine signal quality:
RSSI
> -70 dBm
-70 dBm to -85 dBm
-86 dBm to -100 dBm
With 4G LTE, operators can now take advantage of three new metrics to help indicate when the device has received
a "good" LTE signal:
Reference Signal Received Power
Reference Signal Received Quality
Signal to Interference and Noise Ratio
channel. As the name implies, SINR is the strength of the signal divided by the strength of any interference.
These parameters may vary depending on the technology being used. The following table describes the RF
conditions that each value range represents.
Meter Engineers Handbook for Cellular Communication
Signal Strength
Excellent
Good
Poor
– RSSP indicates the signal strength and is roughly analogous to RSSI.
– RSRQ describes the signal quality and is similar to Ec/Io.
– SINR (also called SNR) indicates the throughput capacity of the
Ec/lo Signal Quality
0 to -6 Excellent
-7 to -10 Good
-11 to -20 Fair to Poor
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