Direct-sequence spread spectrum spectral overlay in the instrument landing system glideslope and microwave landing system bands

We compare the performance of direct-sequence spread spectrum (DS-SS) code-division multiple access (CDMA) systems used in spectral overlay mode in two different aeronautical bands: the instrument landing system glideslope (ILS-GS) band, from 329-335 MHz, and the microwave landing system (MLS) band, from 5091-5150 MHz. The purpose of the overlay system is to enable increased spectral efficiency (higher data throughput), for future potential aeronautical data link communications. The effect of the DS-SS system upon the existing aeronautical system (ILS-GS or MLS) is also briefly addressed. Beginning with basic physical characteristics of the two bands, and classical communications analyses, we estimate the potential data rates in both bands for a range of transmit powers, antenna gains, bit error ratios (BER), and example ILS-GS, MLS, and CDMA system parameters. Our comparison uses both analysis and numerical evaluation. We illustrate that while the ILS-GS band offers more favorable propagation conditions, the MLS band offers significantly higher throughputs.