Road tunnel repeaters

We’re currently trying to get network connection in to a road tunnel(up to 10-15km long, with turns, altitude changes etc) during the construction phase for voip / VoLTE use. Our plan is to use multiple RB922UAGS-5HPacD as “repeater stations” throughout the tunnel. The first station will be placed outside the tunnel, with access to the internet through either Ethernet or a LTE-dongle.

The issue is what kind of a “deployment” we should aim for. As we see it, there are two alternatives in which this can be done;

Every X km we use a “repeaterstation” that features 2 x RB922 with high gain directional horns pointing in each direction (one horn per rb922 - and ethernet cable between the two rb922) - How this would be set up in the routerOS software i am not sure. Is there a possiblity of using the WDS mesh feature, but where there are ethernet links in between? Alternatively, since mesh networks themselves may not always be optimal, is there a way to “bridge” the connections through all of the jumps neccessary?

Every Y km we use a “meshstation” that is 1x RB922 with omni-antenna. Setup is “simple” WDS mesh. (Y km must be much lower than X km) - Seems like a much simpler solution but at reduced throughput and more units.

See the attached photo for a visual drawing of the alternatives.
2017-04-11 10.01.09.jpg

Alt 1 should give you better performance and a more stable network but it will cost more.

Alt 2 will be quick to setup and cheaper, but the omni antennas may have issues with latency/ccq

The ideal solution I think would be fibre. Other companies could even re use it for cctv ect when the construction is finished.