A concept of an air interface for the downlink of an indoor mobile radio system with code-division multiple access (CDMA) based on chirp modulation is presented. A homogenous occupation of the total available bandwidth can be guaranteed forarbitrary signature sequences of the different users. A cost-efficient noncoherent demodulation scheme is presented and analyzed in terms of the bit-error rates for both frequency-nonselective and frequency-selective transmission channels. The analogsignal processing includes chirp matched filtering and a post-detection integration, while the code correlation is carried out in the digital domain. Monte-Carlo simulations of a typical application, like e.g. the auto-identification with active microwave tags in the car industry, indicate that the scheme is robust against multiple-access interference and able to overcome the problem of frequency-selective fading.
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