Spectral overlay of direct-sequence spread spectrum in the instrument landing system glidescope band for airborne Internet

We examine the effects of intentional spectral overlay between a direct-sequence spread spectrum (DS-SS) code-division multiple-access (CDMA) system and the glide scope signal of the Instrument Landing System (ILS) currently employed by the Federal Aviation Administration (FAA). The purpose of the overlay system is to enable increased spectral efficiency (higher data throughput), for future potential aeronautical datalink communications, e.g., an "airborne Internet." That is, this overlay would enable simultaneous use of the ILS band by the current glide slope systems and a new DS-SS CDMA digital communication system. We estimate the performance degradation incurred by both systems for a range of transmit powers, DS-SS bandwidths and data rates, and typical ILS and CDMA system parameters. Our study uses both analysis and computer simulations. The use of the CDMA system as a possible air-to-air (GA) data link is examined, and we provide examples that explore both ILS and CDMA system parameter values appropriate for the successful application of the overlay technique.