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The worldwide installed analog broadcast networks suffer from problems in quality, power consumption, and waste of frequency spectrum. They will be replaced by digital networks in the next century. For analog networks, the planning parameters for frequency, power, and site assignment are well known. For digital audio broadcasting (DAB) networks, the research of the relevant criteria has just started. This paper presents the derivation of protection ratios and field strength levels under worst case conditions for Eureka 147 orthogonal frequency division multiplex (OFDM)-based digital audio broadcast systems from the bit error rate (BER) of the unprotected propagation channel. The channel is characterized by a three-dimensional (3-D) ray optical wave-propagation model. The peculiarities of the resulting multipath field strength delay spectra in single-frequency networks (SFN's) for the calculation of the signal-to-noise ratio (SNR) and the BER at the receiver are discussed. Different terrain types and frequencies are considered. A statistical analysis of the relationship between the SNR and BER leads to the determination of the cochannel protection ratio. An expansion thereof results in the adjacent-channel protection ratios. The minimum required field strength is derived from the protection ratios and the BER's. The influence of different spatial and temporal probabilities is investigated. Examples are shown for verification at 230 and 1472 MHz. Index Terms - Bit error rate, channel characterization, digital audio broadcasting, protection ratio.