[ENB] No SIB7 support for broadcasting GERAN neighbors

[laf0rge]

In any network that involves generations/technology, one typically needs to advertise so-called Inter-RAT neighbor cells. So in GSM, we broadcast UMTS + LTE neighbors, and subsequently in LTE, one needs to broadcast GSM and UMTS neighbors. This is required for proper idle mode cell reselection to work, if (what's always the case in reality) your network coverage of different technologies is not identical, e.g. LTE smaller than GSM or vice versa.

In LTE this is done in SIB6 (UTRAN) and SIB7 (GERAN) or even SIB8 (CDMA2000).

srsENB currently lacks the functionality to configure + broadcast any of those neighbors.

I'm currently playing with the code to add support for SIB7 and am opening this ticket to track progress on this feature.

[laf0rge]

The configuration snipped for SIB7 currently looks like this:

sib7 = {
    t_resel_geran = 1;
    carrier_freqs_info_list =
    (
        {
            cell_resel_prio = 0;
            ncc_permitted = 255;
            q_rx_lev_min = 0;
            thresh_x_high = 7;
            thresh_x_low = 7;

            start_arfcn = 871;
            band_ind = "dcs1800";
        }
    );
};

I haven't yet figured out how to add a "further ARFCNs" list using the srsLTE config file parser, but I'm sure it's not hard.