> 2 | Monitoring Radio Link Stability

> Using the AT command AT^SIND an indicator ("lsta") can be specified that configures the module to monitor the stability of its radio downlink.
> Once configured the module will issue URCs providing information on the radio link stability. There are two types of URC provided:

> • | The first type of URC indicates radio link errors. This type of URC is issued for consecutive radio link errors. A so-called error downcounter value (Edv) is decremented by 1 for every consecutive error. Depending on network settings the Edv count down begins at different values between 1 and 10 (on successful signal decoding the Edv is incremented again). The URC is issued as long as Edv has not reached 0, and is smaller than a given <lstaLevel>. The <lstaLevel> is configured with the AT command AT^SIND and can be set to a value between 0 and 10.

> The first type of "lsta"-URC has 0 as indicator value (<indValue>) and provides the current Edv (<lstaEdv>) and received signal strength (<lstaRssi>) of the radio link:
> +CIEV: "lsta", <indValue>, <lstaEdv>, <lstaRssi>

> • | The second type of URC indicates loss of network coverage. If Edv has reached 0 the module has lost its radio link and will start the cell re-selection process. The module scans its neighboring cells and issues an URC with information on the scanned radio frequencies. In case the neighboring cell scan is not successful, the module continues with a full band scan, i.e., registering a maximum of 40 ARFCNs for which the signal strength is at least above the minimum received power level. The URC is issued for a second time with the results of the full band scan.

> The second type of "lsta"-URC has 1 as indicator value (<indValue>) and provides the number of scanned frequency channels (<lstaNo>), the maximum frequency value (<lstaMax>), the minimum frequency value (<lstaMin>), the mean of the scanned values (<lstaMean>) as well as the variance of the frequency values (<lstaVar>):
> +CIEV: "lsta", <indValue>, <lstaNo>, <lstaMax>, <lstaMin>, <lstaMean>, <lstaVar>
> Note: The first type of URC is not available during active voice or data call connections. In this case only the second type of URC will be issued should the radio link be disturbed or lost. Both URCs are not available in Airplane mode.
> For more information on the AT command AT^SIND and the link stability URCs see also [1].
> The following Figure 1 illustrates the sequence of URCs during IDLE mode in case the module’s radio downlink is interfered with by a jammer.
> Figure 1: Radio link stability monitoring