TDMA and CDMA Capacities in Air-Ground Communications

Weevaluatethecapacitiesofcodedivisionmultipleaccess(CDMA)andtimedivisionmultipleaccess(TDMA)schemesinanaeronauticalenvironment.Themodelfortheenvironment is a three-dimensional cellular arrangement, analogous to the two-dimensional model used for terrestrial cellular radio. The transmission schemes we consider are based upon those of terrestrial cellular, suitably modified to accommodate the unique requirements of pilot-tocontroller communications in civilian air-to-ground communication settings. In accounting forthenearfree-spacepropagationofinterference,weemploynewparametervaluesrequired for the estimation of capacities in the aeronautical environment: theTDMA frequency re-use factorandtheCDMAoutsidecellinterferencefactor.Baseduponthemodifiedterrestrialcellular schemes and these new parameters, we show that if average interference is considered, CDMA capacity is largest. If worst-case interference is considered, the half-duplex TDMA capacity is comparable to the CDMA capacity when the CDMA system uses rebroadcast of air-ground transmissions in the ground-air link, but if this rebroadcast mode is not used, worst-case CDMA capacity is also larger than worst-case TDMA capacity.