PC-12
Air Traffic Control Fully Certified
Communication Breakdown
ATC Issue All Types
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings
A PC-12 was inbound level at 12;000 [feet]. He came to my frequency and I could hear him loud and clear. I responded several times but the pilot could not hear me. It became apparent the pilot could hear some garbled transmissions from me because of the responses he gave. I passed a message through an airborne aircraft and the pilot could hear them loud and clear. I could not keep relaying through a secondary aircraft as they needed to be on another frequency and I needed my frequency back. The PC-12 decided they would just change to advisory frequency on their own and began descending and violated restricted airspace as well; all without cancelling IFR. I finally established radio contact as they drifted closer. We need a relay antenna at OLS. We have a lot of IFR aircraft in and out as well as many international flights over the boarder. We can not communicate with the  pilots and it is creating too many problems. Controllers should not be left helpless with such an easily fixable situation.
A PC-12 called south of the US/Mexico border inbound to OLS. The pilot called several times; eventually crossing the border; but could not hear me and stated he would start descending for the airport. The aircraft was at 12;000 feet and the reported ceilings were at 6;000 feet. The aircraft entered a restricted area (R2303B) at 12;000 feet and started to descend. About 12 miles northeast of the airport; the pilot could hear me and I gave him an altitude to climb to; since he was now below the MVA; and issued vectors back to the destination airport. We have had numerous communications issues with aircraft inbound from Mexico landing at OLS. We need a radio transceiver at the OLS airport. We have no RADAR coverage below 8;000 feet within 10 miles of the airport; the radio problem makes this very dangerous.
U90 Controller described an airspace incursion event when communications was lost with traffic inbound from Mexico to OLS could; the reporter suggesting improved communications equipment at OLS.