Feasibility of Cell Planning for the L-Band Digital Aeronautical Communications System Under the Constraint of Secondary Spectrum Usage

The L-band digital aeronautical communications system (LDACS) is a cellular air-ground data link for air traffic control. It is a cornerstone of the future aeronautical communications infrastructure. LDACS shall operate in the frequency band 960-1164 MHz under the constraint of secondary spectrum usage. This implies strict spectral, power, and spatial separation toward current legacy systems operating in this frequency band. It has been proposed to fulfil these restrictions using cell planning for LDACS without changing frequency allocations of the legacy systems. However, the feasibility of such a cell planning is yet to be demonstrated. In this paper, we demonstrate the feasibility of LDACS cell planning under these constraints. For this purpose, we introduce the theoretical limits for such a separation enabling the coexistence of LDACS and distance measuring equipment (DME: the primary user) system in the same frequency band. Closed-form expressions are obtained such that the proper operation of DME is not harmfully affected by LDACS. These expressions are utilized in the first step to find DME-compliant locations for LDACS ground stations. In the second step, interference constraints within LDACS itself are defined and applied. This approach yields DME-compliant locations of LDACS ground stations with channel assignments fulfilling the interference constraints. The application of our method shows that LDACS cell planning in Europe is possible without disturbing the proper operation of the DME system.