For the real wizards in wireless out there in the wilderness, here's an interesting challenge.
I'm considering an underground (non-gaseous, non-explosive) wireless PtP network, intended to serve as a wireless back-haul for other services. Actual wireless communications is accomplished using a different, dedicated voice radio system (low frequency), whose repeaters are networked via our wireless PtP network, as illustrated by the 'cells' in the included drawing.
Imagine if you will, extremely long and quite regular corridors, in which we'll establish PtP links. At certain corridor junctures, we'll turn at a right angle to extend the network. In some corridors, we'll need to have PtP links back-to-back, so we're able to add right-angle 'spurs' to the network.
I've searched the forum for input on what is the best solutions for mulitlink PtP links, and see only the thread from October 2012 regarding nv2 issues. It does seem that a TDMA structure might be best for an exclusively back-haul link (no multi-access required), but capacity is not the foremost requirement. Network robustness and minimal, consistent delay are the top priorities.
Radios used at PtP nodes will be directional MIMO, with the back-sides shielded to minimize interference from the link radio in opposite/other direction. Directional antennas are chosen to direct signal and enable minimum transmit power - hopefully improving interference mitigation.
Frequency use/re-use will be trialed to minimize interference/co-channel interference, with particular concern on extended links (back-to-back, PtP links) in the same corridor, obviously.
Now wizards, step up, please.
First, I have found almost no postings regarding multilink PtP bridge links in general in the forum (the October, 2012 nv2 post being the only one I've found), so any pointers to relevant posts I've missed would be a great start.
Second, what is the best/recommended protocol/configuration construction of a many link, multilink PtP bridge? (I've seen this referenced as a 'string-of-pearls' but can't find much useful info) I gather that nv2 is not a good choice, except for perhaps the end link(s). The longest multilink I've constructed to date is 3 links in length - and it is nv2. I've not tested it's max throughput, but it is very stable.
Third, what's the longest - most end-to-end links - PtP bridge link you've installed, and what were the issues/best solutions? Some of these bridge links could be 10-12 PtP links in total end-to-end length.
Fourth, has anyone done an underground wireless installation? Experiences to share?
Fifth, could a 'bridge' be constructed so that all radios/routers (and voice repeaters on ether ports) would be on the same sub-net, to minimize packet processing and delay, or is routing required, given the 'complexity' of this network? Preserving MAC addresses is desirable.
Sixth, an alternative architecture could be to use WDS, with each 'node' an Access Point, but then I lose directional antennas and have to operate on a single frequency, correct? This seems problematic as well, as self-interference in these long corridors looks likely to be a big problem, and Omni antennas don't provide any 'directional' selectivity. But, maybe WDS MESH might be a plausible alternative to multilinks. Thoughts or experience on this?
Here's a thought, maybe crazy - anyone ever try to build/use a MIMO Access Point with directional, single polarity antennas connected, and pointing in different directions? You could get H vs V polarization differentiation on back-to-back, linear multilink connections, which should help with self-interference.
Thanks (and much Karma) in advance for any and all input.