Broadcasting systems have to deal with channel variability in order to offer the best spectral efficiency to the receivers. However, the transmission parameters that maximise the spectral efficiency generally leads to a large link unavailability. In this paper, we study analytically the tradeoff between spectral efficiency and coverage for various channel resource allocation strategies when broadcasting two services. More precisely, we consider the following strategies: time sharing, hierarchical modulation and bit division multiplexing. Our main contribution is the combination of bit division multiplexing with non-uniform QAM to improve the performance of broadcasting systems. The results show that this scheme outperforms all the previous channel resource allocation strategies.